llvm/lib/CodeGen/MachinePipeliner.cpp

//===- MachinePipeliner.cpp - Machine Software Pipeliner Pass -------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// An implementation of the Swing Modulo Scheduling (SMS) software pipeliner.
//
// This SMS implementation is a target-independent back-end pass. When enabled,
// the pass runs just prior to the register allocation pass, while the machine
// IR is in SSA form. If software pipelining is successful, then the original
// loop is replaced by the optimized loop. The optimized loop contains one or
// more prolog blocks, the pipelined kernel, and one or more epilog blocks. If
// the instructions cannot be scheduled in a given MII, we increase the MII by
// one and try again.
//
// The SMS implementation is an extension of the ScheduleDAGInstrs class. We
// represent loop carried dependences in the DAG as order edges to the Phi
// nodes. We also perform several passes over the DAG to eliminate unnecessary
// edges that inhibit the ability to pipeline. The implementation uses the
// DFAPacketizer class to compute the minimum initiation interval and the check
// where an instruction may be inserted in the pipelined schedule.
//
// In order for the SMS pass to work, several target specific hooks need to be
// implemented to get information about the loop structure and to rewrite
// instructions.
//
//===----------------------------------------------------------------------===//

#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/PriorityQueue.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/SmallSet.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/iterator_range.h"
#include "llvm/Analysis/AliasAnalysis.h"
#include "llvm/Analysis/MemoryLocation.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/CodeGen/DFAPacketizer.h"
#include "llvm/CodeGen/LiveIntervals.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/MachineDominators.h"
#include "llvm/CodeGen/MachineFunction.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
#include "llvm/CodeGen/MachineInstr.h"
#include "llvm/CodeGen/MachineInstrBuilder.h"
#include "llvm/CodeGen/MachineLoopInfo.h"
#include "llvm/CodeGen/MachineMemOperand.h"
#include "llvm/CodeGen/MachineOperand.h"
#include "llvm/CodeGen/MachinePipeliner.h"
#include "llvm/CodeGen/MachineRegisterInfo.h"
#include "llvm/CodeGen/ModuloSchedule.h"
#include "llvm/CodeGen/RegisterPressure.h"
#include "llvm/CodeGen/ScheduleDAG.h"
#include "llvm/CodeGen/ScheduleDAGMutation.h"
#include "llvm/CodeGen/TargetOpcodes.h"
#include "llvm/CodeGen/TargetRegisterInfo.h"
#include "llvm/CodeGen/TargetSubtargetInfo.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/IR/Attributes.h"
#include "llvm/IR/DebugLoc.h"
#include "llvm/IR/Function.h"
#include "llvm/MC/LaneBitmask.h"
#include "llvm/MC/MCInstrDesc.h"
#include "llvm/MC/MCInstrItineraries.h"
#include "llvm/MC/MCRegisterInfo.h"
#include "llvm/Pass.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
#include <climits>
#include <cstdint>
#include <deque>
#include <functional>
#include <iterator>
#include <map>
#include <memory>
#include <tuple>
#include <utility>
#include <vector>

using namespace llvm;

#define DEBUG_TYPE "pipeliner"

STATISTIC(NumTrytoPipeline, "Number of loops that we attempt to pipeline");
STATISTIC(NumPipelined, "Number of loops software pipelined");
STATISTIC(NumNodeOrderIssues, "Number of node order issues found");
STATISTIC(NumFailBranch, "Pipeliner abort due to unknown branch");
STATISTIC(NumFailLoop, "Pipeliner abort due to unsupported loop");
STATISTIC(NumFailPreheader, "Pipeliner abort due to missing preheader");
STATISTIC(NumFailLargeMaxMII, "Pipeliner abort due to MaxMII too large");
STATISTIC(NumFailZeroMII, "Pipeliner abort due to zero MII");
STATISTIC(NumFailNoSchedule, "Pipeliner abort due to no schedule found");
STATISTIC(NumFailZeroStage, "Pipeliner abort due to zero stage");
STATISTIC(NumFailLargeMaxStage, "Pipeliner abort due to too many stages");

/// A command line option to turn software pipelining on or off.
static cl::opt<bool> EnableSWP("enable-pipeliner", cl::Hidden, cl::init(true),
                               cl::ZeroOrMore,
                               cl::desc("Enable Software Pipelining"));

/// A command line option to enable SWP at -Os.
static cl::opt<bool> EnableSWPOptSize("enable-pipeliner-opt-size",
                                      cl::desc("Enable SWP at Os."), cl::Hidden,
                                      cl::init(false));

/// A command line argument to limit minimum initial interval for pipelining.
static cl::opt<int> SwpMaxMii("pipeliner-max-mii",
                              cl::desc("Size limit for the MII."),
                              cl::Hidden, cl::init(27));

/// A command line argument to limit the number of stages in the pipeline.
static cl::opt<int>
    SwpMaxStages("pipeliner-max-stages",
                 cl::desc("Maximum stages allowed in the generated scheduled."),
                 cl::Hidden, cl::init(3));

/// A command line option to disable the pruning of chain dependences due to
/// an unrelated Phi.
static cl::opt<bool>
    SwpPruneDeps("pipeliner-prune-deps",
                 cl::desc("Prune dependences between unrelated Phi nodes."),
                 cl::Hidden, cl::init(true));

/// A command line option to disable the pruning of loop carried order
/// dependences.
static cl::opt<bool>
    SwpPruneLoopCarried("pipeliner-prune-loop-carried",
                        cl::desc("Prune loop carried order dependences."),
                        cl::Hidden, cl::init(true));

#ifndef NDEBUG
static cl::opt<int> SwpLoopLimit("pipeliner-max", cl::Hidden, cl::init(-1));
#endif

static cl::opt<bool> SwpIgnoreRecMII("pipeliner-ignore-recmii",
                                     cl::ReallyHidden, cl::init(false),
                                     cl::ZeroOrMore, cl::desc("Ignore RecMII"));

static cl::opt<bool> SwpShowResMask("pipeliner-show-mask", cl::Hidden,
                                    cl::init(false));
static cl::opt<bool> SwpDebugResource("pipeliner-dbg-res", cl::Hidden,
                                      cl::init(false));

static cl::opt<bool> EmitTestAnnotations(
    "pipeliner-annotate-for-testing", cl::Hidden, cl::init(false),
    cl::desc("Instead of emitting the pipelined code, annotate instructions "
             "with the generated schedule for feeding into the "
             "-modulo-schedule-test pass"));

static cl::opt<bool> ExperimentalCodeGen(
    "pipeliner-experimental-cg", cl::Hidden, cl::init(false),
    cl::desc(
        "Use the experimental peeling code generator for software pipelining"));

namespace llvm {

// A command line option to enable the CopyToPhi DAG mutation.
cl::opt<bool>
    SwpEnableCopyToPhi("pipeliner-enable-copytophi", cl::ReallyHidden,
                       cl::init(true), cl::ZeroOrMore,
                       cl::desc("Enable CopyToPhi DAG Mutation"));

} // end namespace llvm

unsigned SwingSchedulerDAG::Circuits::MaxPaths = 5;
char MachinePipeliner::ID = 0;
#ifndef NDEBUG
int MachinePipeliner::NumTries = 0;
#endif
char &llvm::MachinePipelinerID = MachinePipeliner::ID;

INITIALIZE_PASS_BEGIN(MachinePipeliner, DEBUG_TYPE,
                      "Modulo Software Pipelining", false, false)
INITIALIZE_PASS_DEPENDENCY(AAResultsWrapperPass)
INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
INITIALIZE_PASS_DEPENDENCY(MachineDominatorTree)
INITIALIZE_PASS_DEPENDENCY(LiveIntervals)
INITIALIZE_PASS_END(MachinePipeliner, DEBUG_TYPE,
                    "Modulo Software Pipelining", false, false)

/// The "main" function for implementing Swing Modulo Scheduling.
bool MachinePipeliner::runOnMachineFunction(MachineFunction &mf) {
  if (skipFunction(mf.getFunction()))
    return false;

  if (!EnableSWP)
    return false;

  if (mf.getFunction().getAttributes().hasAttribute(
          AttributeList::FunctionIndex, Attribute::OptimizeForSize) &&
      !EnableSWPOptSize.getPosition())
    return false;

  if (!mf.getSubtarget().enableMachinePipeliner())
    return false;

  // Cannot pipeline loops without instruction itineraries if we are using
  // DFA for the pipeliner.
  if (mf.getSubtarget().useDFAforSMS() &&
      (!mf.getSubtarget().getInstrItineraryData() ||
       mf.getSubtarget().getInstrItineraryData()->isEmpty()))
    return false;

  MF = &mf;
  MLI = &getAnalysis<MachineLoopInfo>();
  MDT = &getAnalysis<MachineDominatorTree>();
  TII = MF->getSubtarget().getInstrInfo();
  RegClassInfo.runOnMachineFunction(*MF);

  for (auto &L : *MLI)
    scheduleLoop(*L);

  return false;
}

/// Attempt to perform the SMS algorithm on the specified loop. This function is
/// the main entry point for the algorithm.  The function identifies candidate
/// loops, calculates the minimum initiation interval, and attempts to schedule
/// the loop.
bool MachinePipeliner::scheduleLoop(MachineLoop &L) {
  bool Changed = false;
  for (auto &InnerLoop : L)
    Changed |= scheduleLoop(*InnerLoop);

#ifndef NDEBUG
  // Stop trying after reaching the limit (if any).
  int Limit = SwpLoopLimit;
  if (Limit >= 0) {
    if (NumTries >= SwpLoopLimit)
      return Changed;
    NumTries++;
  }
#endif

  setPragmaPipelineOptions(L);
  if (!canPipelineLoop(L)) {
    LLVM_DEBUG(dbgs() << "\n!!! Can not pipeline loop.\n");
    return Changed;
  }

  ++NumTrytoPipeline;

  Changed = swingModuloScheduler(L);

  return Changed;
}

void MachinePipeliner::setPragmaPipelineOptions(MachineLoop &L) {
  MachineBasicBlock *LBLK = L.getTopBlock();

  if (LBLK == nullptr)
    return;

  const BasicBlock *BBLK = LBLK->getBasicBlock();
  if (BBLK == nullptr)
    return;

  const Instruction *TI = BBLK->getTerminator();
  if (TI == nullptr)
    return;

  MDNode *LoopID = TI->getMetadata(LLVMContext::MD_loop);
  if (LoopID == nullptr)
    return;

  assert(LoopID->getNumOperands() > 0 && "requires atleast one operand");
  assert(LoopID->getOperand(0) == LoopID && "invalid loop");

  for (unsigned i = 1, e = LoopID->getNumOperands(); i < e; ++i) {
    MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));

    if (MD == nullptr)
      continue;

    MDString *S = dyn_cast<MDString>(MD->getOperand(0));

    if (S == nullptr)
      continue;

    if (S->getString() == "llvm.loop.pipeline.initiationinterval") {
      assert(MD->getNumOperands() == 2 &&
             "Pipeline initiation interval hint metadata should have two operands.");
      II_setByPragma =
          mdconst::extract<ConstantInt>(MD->getOperand(1))->getZExtValue();
      assert(II_setByPragma >= 1 && "Pipeline initiation interval must be positive.");
    } else if (S->getString() == "llvm.loop.pipeline.disable") {
      disabledByPragma = true;
    }
  }
}

/// Return true if the loop can be software pipelined.  The algorithm is
/// restricted to loops with a single basic block.  Make sure that the
/// branch in the loop can be analyzed.
bool MachinePipeliner::canPipelineLoop(MachineLoop &L) {
  if (L.getNumBlocks() != 1)
    return false;

  if (disabledByPragma)
    return false;

  // Check if the branch can't be understood because we can't do pipelining
  // if that's the case.
  LI.TBB = nullptr;
  LI.FBB = nullptr;
  LI.BrCond.clear();
  if (TII->analyzeBranch(*L.getHeader(), LI.TBB, LI.FBB, LI.BrCond)) {
    LLVM_DEBUG(
        dbgs() << "Unable to analyzeBranch, can NOT pipeline current Loop\n");
    NumFailBranch++;
    return false;
  }

  LI.LoopInductionVar = nullptr;
  LI.LoopCompare = nullptr;
  if (!TII->analyzeLoopForPipelining(L.getTopBlock())) {
    LLVM_DEBUG(
        dbgs() << "Unable to analyzeLoop, can NOT pipeline current Loop\n");
    NumFailLoop++;
    return false;
  }

  if (!L.getLoopPreheader()) {
    LLVM_DEBUG(
        dbgs() << "Preheader not found, can NOT pipeline current Loop\n");
    NumFailPreheader++;
    return false;
  }

  // Remove any subregisters from inputs to phi nodes.
  preprocessPhiNodes(*L.getHeader());
  return true;
}

void MachinePipeliner::preprocessPhiNodes(MachineBasicBlock &B) {
  MachineRegisterInfo &MRI = MF->getRegInfo();
  SlotIndexes &Slots = *getAnalysis<LiveIntervals>().getSlotIndexes();

  for (MachineInstr &PI : make_range(B.begin(), B.getFirstNonPHI())) {
    MachineOperand &DefOp = PI.getOperand(0);
    assert(DefOp.getSubReg() == 0);
    auto *RC = MRI.getRegClass(DefOp.getReg());

    for (unsigned i = 1, n = PI.getNumOperands(); i != n; i += 2) {
      MachineOperand &RegOp = PI.getOperand(i);
      if (RegOp.getSubReg() == 0)
        continue;

      // If the operand uses a subregister, replace it with a new register
      // without subregisters, and generate a copy to the new register.
      Register NewReg = MRI.createVirtualRegister(RC);
      MachineBasicBlock &PredB = *PI.getOperand(i+1).getMBB();
      MachineBasicBlock::iterator At = PredB.getFirstTerminator();
      const DebugLoc &DL = PredB.findDebugLoc(At);
      auto Copy = BuildMI(PredB, At, DL, TII->get(TargetOpcode::COPY), NewReg)
                    .addReg(RegOp.getReg(), getRegState(RegOp),
                            RegOp.getSubReg());
      Slots.insertMachineInstrInMaps(*Copy);
      RegOp.setReg(NewReg);
      RegOp.setSubReg(0);
    }
  }
}

/// The SMS algorithm consists of the following main steps:
/// 1. Computation and analysis of the dependence graph.
/// 2. Ordering of the nodes (instructions).
/// 3. Attempt to Schedule the loop.
bool MachinePipeliner::swingModuloScheduler(MachineLoop &L) {
  assert(L.getBlocks().size() == 1 && "SMS works on single blocks only.");

  SwingSchedulerDAG SMS(*this, L, getAnalysis<LiveIntervals>(), RegClassInfo,
                        II_setByPragma);

  MachineBasicBlock *MBB = L.getHeader();
  // The kernel should not include any terminator instructions.  These
  // will be added back later.
  SMS.startBlock(MBB);

  // Compute the number of 'real' instructions in the basic block by
  // ignoring terminators.
  unsigned size = MBB->size();
  for (MachineBasicBlock::iterator I = MBB->getFirstTerminator(),
                                   E = MBB->instr_end();
       I != E; ++I, --size)
    ;

  SMS.enterRegion(MBB, MBB->begin(), MBB->getFirstTerminator(), size);
  SMS.schedule();
  SMS.exitRegion();

  SMS.finishBlock();
  return SMS.hasNewSchedule();
}

void SwingSchedulerDAG::setMII(unsigned ResMII, unsigned RecMII) {
  if (II_setByPragma > 0)
    MII = II_setByPragma;
  else
    MII = std::max(ResMII, RecMII);
}

void SwingSchedulerDAG::setMAX_II() {
  if (II_setByPragma > 0)
    MAX_II = II_setByPragma;
  else
    MAX_II = MII + 10;
}

/// We override the schedule function in ScheduleDAGInstrs to implement the
/// scheduling part of the Swing Modulo Scheduling algorithm.
void SwingSchedulerDAG::schedule() {
  AliasAnalysis *AA = &Pass.getAnalysis<AAResultsWrapperPass>().getAAResults();
  buildSchedGraph(AA);
  addLoopCarriedDependences(AA);
  updatePhiDependences();
  Topo.InitDAGTopologicalSorting();
  changeDependences();
  postprocessDAG();
  LLVM_DEBUG(dump());

  NodeSetType NodeSets;
  findCircuits(NodeSets);
  NodeSetType Circuits = NodeSets;

  // Calculate the MII.
  unsigned ResMII = calculateResMII();
  unsigned RecMII = calculateRecMII(NodeSets);

  fuseRecs(NodeSets);

  // This flag is used for testing and can cause correctness problems.
  if (SwpIgnoreRecMII)
    RecMII = 0;

  setMII(ResMII, RecMII);
  setMAX_II();

  LLVM_DEBUG(dbgs() << "MII = " << MII << " MAX_II = " << MAX_II
                    << " (rec=" << RecMII << ", res=" << ResMII << ")\n");

  // Can't schedule a loop without a valid MII.
  if (MII == 0) {
    LLVM_DEBUG(
        dbgs()
        << "0 is not a valid Minimal Initiation Interval, can NOT schedule\n");
    NumFailZeroMII++;
    return;
  }

  // Don't pipeline large loops.
  if (SwpMaxMii != -1 && (int)MII > SwpMaxMii) {
    LLVM_DEBUG(dbgs() << "MII > " << SwpMaxMii
                      << ", we don't pipleline large loops\n");
    NumFailLargeMaxMII++;
    return;
  }

  computeNodeFunctions(NodeSets);

  registerPressureFilter(NodeSets);

  colocateNodeSets(NodeSets);

  checkNodeSets(NodeSets);

  LLVM_DEBUG({
    for (auto &I : NodeSets) {
      dbgs() << "  Rec NodeSet ";
      I.dump();
    }
  });

  llvm::stable_sort(NodeSets, std::greater<NodeSet>());

  groupRemainingNodes(NodeSets);

  removeDuplicateNodes(NodeSets);

  LLVM_DEBUG({
    for (auto &I : NodeSets) {
      dbgs() << "  NodeSet ";
      I.dump();
    }
  });

  computeNodeOrder(NodeSets);

  // check for node order issues
  checkValidNodeOrder(Circuits);

  SMSchedule Schedule(Pass.MF);
  Scheduled = schedulePipeline(Schedule);

  if (!Scheduled){
    LLVM_DEBUG(dbgs() << "No schedule found, return\n");
    NumFailNoSchedule++;
    return;
  }

  unsigned numStages = Schedule.getMaxStageCount();
  // No need to generate pipeline if there are no overlapped iterations.
  if (numStages == 0) {
    LLVM_DEBUG(
        dbgs() << "No overlapped iterations, no need to generate pipeline\n");
    NumFailZeroStage++;
    return;
  }
  // Check that the maximum stage count is less than user-defined limit.
  if (SwpMaxStages > -1 && (int)numStages > SwpMaxStages) {
    LLVM_DEBUG(dbgs() << "numStages:" << numStages << ">" << SwpMaxStages
                      << " : too many stages, abort\n");
    NumFailLargeMaxStage++;
    return;
  }

  // Generate the schedule as a ModuloSchedule.
  DenseMap<MachineInstr *, int> Cycles, Stages;
  std::vector<MachineInstr *> OrderedInsts;
  for (int Cycle = Schedule.getFirstCycle(); Cycle <= Schedule.getFinalCycle();
       ++Cycle) {
    for (SUnit *SU : Schedule.getInstructions(Cycle)) {
      OrderedInsts.push_back(SU->getInstr());
      Cycles[SU->getInstr()] = Cycle;
      Stages[SU->getInstr()] = Schedule.stageScheduled(SU);
    }
  }
  DenseMap<MachineInstr *, std::pair<unsigned, int64_t>> NewInstrChanges;
  for (auto &KV : NewMIs) {
    Cycles[KV.first] = Cycles[KV.second];
    Stages[KV.first] = Stages[KV.second];
    NewInstrChanges[KV.first] = InstrChanges[getSUnit(KV.first)];
  }

  ModuloSchedule MS(MF, &Loop, std::move(OrderedInsts), std::move(Cycles),
                    std::move(Stages));
  if (EmitTestAnnotations) {
    assert(NewInstrChanges.empty() &&
           "Cannot serialize a schedule with InstrChanges!");
    ModuloScheduleTestAnnotater MSTI(MF, MS);
    MSTI.annotate();
    return;
  }
  // The experimental code generator can't work if there are InstChanges.
  if (ExperimentalCodeGen && NewInstrChanges.empty()) {
    PeelingModuloScheduleExpander MSE(MF, MS, &LIS);
    // Experimental code generation isn't complete yet, but it can partially
    // validate the code it generates against the original
    // ModuloScheduleExpander.
    MSE.validateAgainstModuloScheduleExpander();
  } else {
    ModuloScheduleExpander MSE(MF, MS, LIS, std::move(NewInstrChanges));
    MSE.expand();
    MSE.cleanup();
  }
  ++NumPipelined;
}

/// Clean up after the software pipeliner runs.
void SwingSchedulerDAG::finishBlock() {
  for (auto &KV : NewMIs)
    MF.DeleteMachineInstr(KV.second);
  NewMIs.clear();

  // Call the superclass.
  ScheduleDAGInstrs::finishBlock();
}

/// Return the register values for  the operands of a Phi instruction.
/// This function assume the instruction is a Phi.
static void getPhiRegs(MachineInstr &Phi, MachineBasicBlock *Loop,
                       unsigned &InitVal, unsigned &LoopVal) {
  assert(Phi.isPHI() && "Expecting a Phi.");

  InitVal = 0;
  LoopVal = 0;
  for (unsigned i = 1, e = Phi.getNumOperands(); i != e; i += 2)
    if (Phi.getOperand(i + 1).getMBB() != Loop)
      InitVal = Phi.getOperand(i).getReg();
    else
      LoopVal = Phi.getOperand(i).getReg();

  assert(InitVal != 0 && LoopVal != 0 && "Unexpected Phi structure.");
}

/// Return the Phi register value that comes the loop block.
static unsigned getLoopPhiReg(MachineInstr &Phi, MachineBasicBlock *LoopBB) {
  for (unsigned i = 1, e = Phi.getNumOperands(); i != e; i += 2)
    if (Phi.getOperand(i + 1).getMBB() == LoopBB)
      return Phi.getOperand(i).getReg();
  return 0;
}

/// Return true if SUb can be reached from SUa following the chain edges.
static bool isSuccOrder(SUnit *SUa, SUnit *SUb) {
  SmallPtrSet<SUnit *, 8> Visited;
  SmallVector<SUnit *, 8> Worklist;
  Worklist.push_back(SUa);
  while (!Worklist.empty()) {
    const SUnit *SU = Worklist.pop_back_val();
    for (auto &SI : SU->Succs) {
      SUnit *SuccSU = SI.getSUnit();
      if (SI.getKind() == SDep::Order) {
        if (Visited.count(SuccSU))
          continue;
        if (SuccSU == SUb)
          return true;
        Worklist.push_back(SuccSU);
        Visited.insert(SuccSU);
      }
    }
  }
  return false;
}

/// Return true if the instruction causes a chain between memory
/// references before and after it.
static bool isDependenceBarrier(MachineInstr &MI, AliasAnalysis *AA) {
  return MI.isCall() || MI.mayRaiseFPException() ||
         MI.hasUnmodeledSideEffects() ||
         (MI.hasOrderedMemoryRef() &&
          (!MI.mayLoad() || !MI.isDereferenceableInvariantLoad(AA)));
}

/// Return the underlying objects for the memory references of an instruction.
/// This function calls the code in ValueTracking, but first checks that the
/// instruction has a memory operand.
static void getUnderlyingObjects(const MachineInstr *MI,
                                 SmallVectorImpl<const Value *> &Objs,
                                 const DataLayout &DL) {
  if (!MI->hasOneMemOperand())
    return;
  MachineMemOperand *MM = *MI->memoperands_begin();
  if (!MM->getValue())
    return;
  GetUnderlyingObjects(MM->getValue(), Objs, DL);
  for (const Value *V : Objs) {
    if (!isIdentifiedObject(V)) {
      Objs.clear();
      return;
    }
    Objs.push_back(V);
  }
}

/// Add a chain edge between a load and store if the store can be an
/// alias of the load on a subsequent iteration, i.e., a loop carried
/// dependence. This code is very similar to the code in ScheduleDAGInstrs
/// but that code doesn't create loop carried dependences.
void SwingSchedulerDAG::addLoopCarriedDependences(AliasAnalysis *AA) {
  MapVector<const Value *, SmallVector<SUnit *, 4>> PendingLoads;
  Value *UnknownValue =
    UndefValue::get(Type::getVoidTy(MF.getFunction().getContext()));
  for (auto &SU : SUnits) {
    MachineInstr &MI = *SU.getInstr();
    if (isDependenceBarrier(MI, AA))
      PendingLoads.clear();
    else if (MI.mayLoad()) {
      SmallVector<const Value *, 4> Objs;
      getUnderlyingObjects(&MI, Objs, MF.getDataLayout());
      if (Objs.empty())
        Objs.push_back(UnknownValue);
      for (auto V : Objs) {
        SmallVector<SUnit *, 4> &SUs = PendingLoads[V];
        SUs.push_back(&SU);
      }
    } else if (MI.mayStore()) {
      SmallVector<const Value *, 4> Objs;
      getUnderlyingObjects(&MI, Objs, MF.getDataLayout());
      if (Objs.empty())
        Objs.push_back(UnknownValue);
      for (auto V : Objs) {
        MapVector<const Value *, SmallVector<SUnit *, 4>>::iterator I =
            PendingLoads.find(V);
        if (I == PendingLoads.end())
          continue;
        for (auto Load : I->second) {
          if (isSuccOrder(Load, &SU))
            continue;
          MachineInstr &LdMI = *Load->getInstr();
          // First, perform the cheaper check that compares the base register.
          // If they are the same and the load offset is less than the store
          // offset, then mark the dependence as loop carried potentially.
          const MachineOperand *BaseOp1, *BaseOp2;
          int64_t Offset1, Offset2;
          if (TII->getMemOperandWithOffset(LdMI, BaseOp1, Offset1, TRI) &&
              TII->getMemOperandWithOffset(MI, BaseOp2, Offset2, TRI)) {
            if (BaseOp1->isIdenticalTo(*BaseOp2) &&
                (int)Offset1 < (int)Offset2) {
              assert(TII->areMemAccessesTriviallyDisjoint(LdMI, MI) &&
                     "What happened to the chain edge?");
              SDep Dep(Load, SDep::Barrier);
              Dep.setLatency(1);
              SU.addPred(Dep);
              continue;
            }
          }
          // Second, the more expensive check that uses alias analysis on the
          // base registers. If they alias, and the load offset is less than
          // the store offset, the mark the dependence as loop carried.
          if (!AA) {
            SDep Dep(Load, SDep::Barrier);
            Dep.setLatency(1);
            SU.addPred(Dep);
            continue;
          }
          MachineMemOperand *MMO1 = *LdMI.memoperands_begin();
          MachineMemOperand *MMO2 = *MI.memoperands_begin();
          if (!MMO1->getValue() || !MMO2->getValue()) {
            SDep Dep(Load, SDep::Barrier);
            Dep.setLatency(1);
            SU.addPred(Dep);
            continue;
          }
          if (MMO1->getValue() == MMO2->getValue() &&
              MMO1->getOffset() <= MMO2->getOffset()) {
            SDep Dep(Load, SDep::Barrier);
            Dep.setLatency(1);
            SU.addPred(Dep);
            continue;
          }
          AliasResult AAResult = AA->alias(
              MemoryLocation(MMO1->getValue(), LocationSize::unknown(),
                             MMO1->getAAInfo()),
              MemoryLocation(MMO2->getValue(), LocationSize::unknown(),
                             MMO2->getAAInfo()));

          if (AAResult != NoAlias) {
            SDep Dep(Load, SDep::Barrier);
            Dep.setLatency(1);
            SU.addPred(Dep);
          }
        }
      }
    }
  }
}

/// Update the phi dependences to the DAG because ScheduleDAGInstrs no longer
/// processes dependences for PHIs. This function adds true dependences
/// from a PHI to a use, and a loop carried dependence from the use to the
/// PHI. The loop carried dependence is represented as an anti dependence
/// edge. This function also removes chain dependences between unrelated
/// PHIs.
void SwingSchedulerDAG::updatePhiDependences() {
  SmallVector<SDep, 4> RemoveDeps;
  const TargetSubtargetInfo &ST = MF.getSubtarget<TargetSubtargetInfo>();

  // Iterate over each DAG node.
  for (SUnit &I : SUnits) {
    RemoveDeps.clear();
    // Set to true if the instruction has an operand defined by a Phi.
    unsigned HasPhiUse = 0;
    unsigned HasPhiDef = 0;
    MachineInstr *MI = I.getInstr();
    // Iterate over each operand, and we process the definitions.
    for (MachineInstr::mop_iterator MOI = MI->operands_begin(),
                                    MOE = MI->operands_end();
         MOI != MOE; ++MOI) {
      if (!MOI->isReg())
        continue;
      Register Reg = MOI->getReg();
      if (MOI->isDef()) {
        // If the register is used by a Phi, then create an anti dependence.
        for (MachineRegisterInfo::use_instr_iterator
                 UI = MRI.use_instr_begin(Reg),
                 UE = MRI.use_instr_end();
             UI != UE; ++UI) {
          MachineInstr *UseMI = &*UI;
          SUnit *SU = getSUnit(UseMI);
          if (SU != nullptr && UseMI->isPHI()) {
            if (!MI->isPHI()) {
              SDep Dep(SU, SDep::Anti, Reg);
              Dep.setLatency(1);
              I.addPred(Dep);
            } else {
              HasPhiDef = Reg;
              // Add a chain edge to a dependent Phi that isn't an existing
              // predecessor.
              if (SU->NodeNum < I.NodeNum && !I.isPred(SU))
                I.addPred(SDep(SU, SDep::Barrier));
            }
          }
        }
      } else if (MOI->isUse()) {
        // If the register is defined by a Phi, then create a true dependence.
        MachineInstr *DefMI = MRI.getUniqueVRegDef(Reg);
        if (DefMI == nullptr)
          continue;
        SUnit *SU = getSUnit(DefMI);
        if (SU != nullptr && DefMI->isPHI()) {
          if (!MI->isPHI()) {
            SDep Dep(SU, SDep::Data, Reg);
            Dep.setLatency(0);
            ST.adjustSchedDependency(SU, &I, Dep);
            I.addPred(Dep);
          } else {
            HasPhiUse = Reg;
            // Add a chain edge to a dependent Phi that isn't an existing
            // predecessor.
            if (SU->NodeNum < I.NodeNum && !I.isPred(SU))
              I.addPred(SDep(SU, SDep::Barrier));
          }
        }
      }
    }
    // Remove order dependences from an unrelated Phi.
    if (!SwpPruneDeps)
      continue;
    for (auto &PI : I.Preds) {
      MachineInstr *PMI = PI.getSUnit()->getInstr();
      if (PMI->isPHI() && PI.getKind() == SDep::Order) {
        if (I.getInstr()->isPHI()) {
          if (PMI->getOperand(0).getReg() == HasPhiUse)
            continue;
          if (getLoopPhiReg(*PMI, PMI->getParent()) == HasPhiDef)
            continue;
        }
        RemoveDeps.push_back(PI);
      }
    }
    for (int i = 0, e = RemoveDeps.size(); i != e; ++i)
      I.removePred(RemoveDeps[i]);
  }
}

/// Iterate over each DAG node and see if we can change any dependences
/// in order to reduce the recurrence MII.
void SwingSchedulerDAG::changeDependences() {
  // See if an instruction can use a value from the previous iteration.
  // If so, we update the base and offset of the instruction and change
  // the dependences.
  for (SUnit &I : SUnits) {
    unsigned BasePos = 0, OffsetPos = 0, NewBase = 0;
    int64_t NewOffset = 0;
    if (!canUseLastOffsetValue(I.getInstr(), BasePos, OffsetPos, NewBase,
                               NewOffset))
      continue;

    // Get the MI and SUnit for the instruction that defines the original base.
    Register OrigBase = I.getInstr()->getOperand(BasePos).getReg();
    MachineInstr *DefMI = MRI.getUniqueVRegDef(OrigBase);
    if (!DefMI)
      continue;
    SUnit *DefSU = getSUnit(DefMI);
    if (!DefSU)
      continue;
    // Get the MI and SUnit for the instruction that defins the new base.
    MachineInstr *LastMI = MRI.getUniqueVRegDef(NewBase);
    if (!LastMI)
      continue;
    SUnit *LastSU = getSUnit(LastMI);
    if (!LastSU)
      continue;

    if (Topo.IsReachable(&I, LastSU))
      continue;

    // Remove the dependence. The value now depends on a prior iteration.
    SmallVector<SDep, 4> Deps;
    for (SUnit::pred_iterator P = I.Preds.begin(), E = I.Preds.end(); P != E;
         ++P)
      if (P->getSUnit() == DefSU)
        Deps.push_back(*P);
    for (int i = 0, e = Deps.size(); i != e; i++) {
      Topo.RemovePred(&I, Deps[i].getSUnit());
      I.removePred(Deps[i]);
    }
    // Remove the chain dependence between the instructions.
    Deps.clear();
    for (auto &P : LastSU->Preds)
      if (P.getSUnit() == &I && P.getKind() == SDep::Order)
        Deps.push_back(P);
    for (int i = 0, e = Deps.size(); i != e; i++) {
      Topo.RemovePred(LastSU, Deps[i].getSUnit());
      LastSU->removePred(Deps[i]);
    }

    // Add a dependence between the new instruction and the instruction
    // that defines the new base.
    SDep Dep(&I, SDep::Anti, NewBase);
    Topo.AddPred(LastSU, &I);
    LastSU->addPred(Dep);

    // Remember the base and offset information so that we can update the
    // instruction during code generation.
    InstrChanges[&I] = std::make_pair(NewBase, NewOffset);
  }
}

namespace {

// FuncUnitSorter - Comparison operator used to sort instructions by
// the number of functional unit choices.
struct FuncUnitSorter {
  const InstrItineraryData *InstrItins;
  const MCSubtargetInfo *STI;
  DenseMap<unsigned, unsigned> Resources;

  FuncUnitSorter(const TargetSubtargetInfo &TSI)
      : InstrItins(TSI.getInstrItineraryData()), STI(&TSI) {}

  // Compute the number of functional unit alternatives needed
  // at each stage, and take the minimum value. We prioritize the
  // instructions by the least number of choices first.
  unsigned minFuncUnits(const MachineInstr *Inst, unsigned &F) const {
    unsigned SchedClass = Inst->getDesc().getSchedClass();
    unsigned min = UINT_MAX;
    if (InstrItins && !InstrItins->isEmpty()) {
      for (const InstrStage &IS :
           make_range(InstrItins->beginStage(SchedClass),
                      InstrItins->endStage(SchedClass))) {
        unsigned funcUnits = IS.getUnits();
        unsigned numAlternatives = countPopulation(funcUnits);
        if (numAlternatives < min) {
          min = numAlternatives;
          F = funcUnits;
        }
      }
      return min;
    }
    if (STI && STI->getSchedModel().hasInstrSchedModel()) {
      const MCSchedClassDesc *SCDesc =
          STI->getSchedModel().getSchedClassDesc(SchedClass);
      if (!SCDesc->isValid())
        // No valid Schedule Class Desc for schedClass, should be
        // Pseudo/PostRAPseudo
        return min;

      for (const MCWriteProcResEntry &PRE :
           make_range(STI->getWriteProcResBegin(SCDesc),
                      STI->getWriteProcResEnd(SCDesc))) {
        if (!PRE.Cycles)
          continue;
        const MCProcResourceDesc *ProcResource =
            STI->getSchedModel().getProcResource(PRE.ProcResourceIdx);
        unsigned NumUnits = ProcResource->NumUnits;
        if (NumUnits < min) {
          min = NumUnits;
          F = PRE.ProcResourceIdx;
        }
      }
      return min;
    }
    llvm_unreachable("Should have non-empty InstrItins or hasInstrSchedModel!");
  }

  // Compute the critical resources needed by the instruction. This
  // function records the functional units needed by instructions that
  // must use only one functional unit. We use this as a tie breaker
  // for computing the resource MII. The instrutions that require
  // the same, highly used, functional unit have high priority.
  void calcCriticalResources(MachineInstr &MI) {
    unsigned SchedClass = MI.getDesc().getSchedClass();
    if (InstrItins && !InstrItins->isEmpty()) {
      for (const InstrStage &IS :
           make_range(InstrItins->beginStage(SchedClass),
                      InstrItins->endStage(SchedClass))) {
        unsigned FuncUnits = IS.getUnits();
        if (countPopulation(FuncUnits) == 1)
          Resources[FuncUnits]++;
      }
      return;
    }
    if (STI && STI->getSchedModel().hasInstrSchedModel()) {
      const MCSchedClassDesc *SCDesc =
          STI->getSchedModel().getSchedClassDesc(SchedClass);
      if (!SCDesc->isValid())
        // No valid Schedule Class Desc for schedClass, should be
        // Pseudo/PostRAPseudo
        return;

      for (const MCWriteProcResEntry &PRE :
           make_range(STI->getWriteProcResBegin(SCDesc),
                      STI->getWriteProcResEnd(SCDesc))) {
        if (!PRE.Cycles)
          continue;
        Resources[PRE.ProcResourceIdx]++;
      }
      return;
    }
    llvm_unreachable("Should have non-empty InstrItins or hasInstrSchedModel!");
  }

  /// Return true if IS1 has less priority than IS2.
  bool operator()(const MachineInstr *IS1, const MachineInstr *IS2) const {
    unsigned F1 = 0, F2 = 0;
    unsigned MFUs1 = minFuncUnits(IS1, F1);
    unsigned MFUs2 = minFuncUnits(IS2, F2);
    if (MFUs1 == MFUs2)
      return Resources.lookup(F1) < Resources.lookup(F2);
    return MFUs1 > MFUs2;
  }
};

} // end anonymous namespace

/// Calculate the resource constrained minimum initiation interval for the
/// specified loop. We use the DFA to model the resources needed for
/// each instruction, and we ignore dependences. A different DFA is created
/// for each cycle that is required. When adding a new instruction, we attempt
/// to add it to each existing DFA, until a legal space is found. If the
/// instruction cannot be reserved in an existing DFA, we create a new one.
unsigned SwingSchedulerDAG::calculateResMII() {

  LLVM_DEBUG(dbgs() << "calculateResMII:\n");
  SmallVector<ResourceManager*, 8> Resources;
  MachineBasicBlock *MBB = Loop.getHeader();
  Resources.push_back(new ResourceManager(&MF.getSubtarget()));

  // Sort the instructions by the number of available choices for scheduling,
  // least to most. Use the number of critical resources as the tie breaker.
  FuncUnitSorter FUS = FuncUnitSorter(MF.getSubtarget());
  for (MachineBasicBlock::iterator I = MBB->getFirstNonPHI(),
                                   E = MBB->getFirstTerminator();
       I != E; ++I)
    FUS.calcCriticalResources(*I);
  PriorityQueue<MachineInstr *, std::vector<MachineInstr *>, FuncUnitSorter>
      FuncUnitOrder(FUS);

  for (MachineBasicBlock::iterator I = MBB->getFirstNonPHI(),
                                   E = MBB->getFirstTerminator();
       I != E; ++I)
    FuncUnitOrder.push(&*I);

  while (!FuncUnitOrder.empty()) {
    MachineInstr *MI = FuncUnitOrder.top();
    FuncUnitOrder.pop();
    if (TII->isZeroCost(MI->getOpcode()))
      continue;
    // Attempt to reserve the instruction in an existing DFA. At least one
    // DFA is needed for each cycle.
    unsigned NumCycles = getSUnit(MI)->Latency;
    unsigned ReservedCycles = 0;
    SmallVectorImpl<ResourceManager *>::iterator RI = Resources.begin();
    SmallVectorImpl<ResourceManager *>::iterator RE = Resources.end();
    LLVM_DEBUG({
      dbgs() << "Trying to reserve resource for " << NumCycles
             << " cycles for \n";
      MI->dump();
    });
    for (unsigned C = 0; C < NumCycles; ++C)
      while (RI != RE) {
        if ((*RI)->canReserveResources(*MI)) {
          (*RI)->reserveResources(*MI);
          ++ReservedCycles;
          break;
        }
        RI++;
      }
    LLVM_DEBUG(dbgs() << "ReservedCycles:" << ReservedCycles
                      << ", NumCycles:" << NumCycles << "\n");
    // Add new DFAs, if needed, to reserve resources.
    for (unsigned C = ReservedCycles; C < NumCycles; ++C) {
      LLVM_DEBUG(if (SwpDebugResource) dbgs()
                 << "NewResource created to reserve resources"
                 << "\n");
      ResourceManager *NewResource = new ResourceManager(&MF.getSubtarget());
      assert(NewResource->canReserveResources(*MI) && "Reserve error.");
      NewResource->reserveResources(*MI);
      Resources.push_back(NewResource);
    }
  }
  int Resmii = Resources.size();
  LLVM_DEBUG(dbgs() << "Retrun Res MII:" << Resmii << "\n");
  // Delete the memory for each of the DFAs that were created earlier.
  for (ResourceManager *RI : Resources) {
    ResourceManager *D = RI;
    delete D;
  }
  Resources.clear();
  return Resmii;
}

/// Calculate the recurrence-constrainted minimum initiation interval.
/// Iterate over each circuit.  Compute the delay(c) and distance(c)
/// for each circuit. The II needs to satisfy the inequality
/// delay(c) - II*distance(c) <= 0. For each circuit, choose the smallest
/// II that satisfies the inequality, and the RecMII is the maximum
/// of those values.
unsigned SwingSchedulerDAG::calculateRecMII(NodeSetType &NodeSets) {
  unsigned RecMII = 0;

  for (NodeSet &Nodes : NodeSets) {
    if (Nodes.empty())
      continue;

    unsigned Delay = Nodes.getLatency();
    unsigned Distance = 1;

    // ii = ceil(delay / distance)
    unsigned CurMII = (Delay + Distance - 1) / Distance;
    Nodes.setRecMII(CurMII);
    if (CurMII > RecMII)
      RecMII = CurMII;
  }

  return RecMII;
}

/// Swap all the anti dependences in the DAG. That means it is no longer a DAG,
/// but we do this to find the circuits, and then change them back.
static void swapAntiDependences(std::vector<SUnit> &SUnits) {
  SmallVector<std::pair<SUnit *, SDep>, 8> DepsAdded;
  for (unsigned i = 0, e = SUnits.size(); i != e; ++i) {
    SUnit *SU = &SUnits[i];
    for (SUnit::pred_iterator IP = SU->Preds.begin(), EP = SU->Preds.end();
         IP != EP; ++IP) {
      if (IP->getKind() != SDep::Anti)
        continue;
      DepsAdded.push_back(std::make_pair(SU, *IP));
    }
  }
  for (SmallVector<std::pair<SUnit *, SDep>, 8>::iterator I = DepsAdded.begin(),
                                                          E = DepsAdded.end();
       I != E; ++I) {
    // Remove this anti dependency and add one in the reverse direction.
    SUnit *SU = I->first;
    SDep &D = I->second;
    SUnit *TargetSU = D.getSUnit();
    unsigned Reg = D.getReg();
    unsigned Lat = D.getLatency();
    SU->removePred(D);
    SDep Dep(SU, SDep::Anti, Reg);
    Dep.setLatency(Lat);
    TargetSU->addPred(Dep);
  }
}

/// Create the adjacency structure of the nodes in the graph.
void SwingSchedulerDAG::Circuits::createAdjacencyStructure(
    SwingSchedulerDAG *DAG) {
  BitVector Added(SUnits.size());
  DenseMap<int, int> OutputDeps;
  for (int i = 0, e = SUnits.size(); i != e; ++i) {
    Added.reset();
    // Add any successor to the adjacency matrix and exclude duplicates.
    for (auto &SI : SUnits[i].Succs) {
      // Only create a back-edge on the first and last nodes of a dependence
      // chain. This records any chains and adds them later.
      if (SI.getKind() == SDep::Output) {
        int N = SI.getSUnit()->NodeNum;
        int BackEdge = i;
        auto Dep = OutputDeps.find(BackEdge);
        if (Dep != OutputDeps.end()) {
          BackEdge = Dep->second;
          OutputDeps.erase(Dep);
        }
        OutputDeps[N] = BackEdge;
      }
      // Do not process a boundary node, an artificial node.
      // A back-edge is processed only if it goes to a Phi.
      if (SI.getSUnit()->isBoundaryNode() || SI.isArtificial() ||
          (SI.getKind() == SDep::Anti && !SI.getSUnit()->getInstr()->isPHI()))
        continue;
      int N = SI.getSUnit()->NodeNum;
      if (!Added.test(N)) {
        AdjK[i].push_back(N);
        Added.set(N);
      }
    }
    // A chain edge between a store and a load is treated as a back-edge in the
    // adjacency matrix.
    for (auto &PI : SUnits[i].Preds) {
      if (!SUnits[i].getInstr()->mayStore() ||
          !DAG->isLoopCarriedDep(&SUnits[i], PI, false))
        continue;
      if (PI.getKind() == SDep::Order && PI.getSUnit()->getInstr()->mayLoad()) {
        int N = PI.getSUnit()->NodeNum;
        if (!Added.test(N)) {
          AdjK[i].push_back(N);
          Added.set(N);
        }
      }
    }
  }
  // Add back-edges in the adjacency matrix for the output dependences.
  for (auto &OD : OutputDeps)
    if (!Added.test(OD.second)) {
      AdjK[OD.first].push_back(OD.second);
      Added.set(OD.second);
    }
}

/// Identify an elementary circuit in the dependence graph starting at the
/// specified node.
bool SwingSchedulerDAG::Circuits::circuit(int V, int S, NodeSetType &NodeSets,
                                          bool HasBackedge) {
  SUnit *SV = &SUnits[V];
  bool F = false;
  Stack.insert(SV);
  Blocked.set(V);

  for (auto W : AdjK[V]) {
    if (NumPaths > MaxPaths)
      break;
    if (W < S)
      continue;
    if (W == S) {
      if (!HasBackedge)
        NodeSets.push_back(NodeSet(Stack.begin(), Stack.end()));
      F = true;
      ++NumPaths;
      break;
    } else if (!Blocked.test(W)) {
      if (circuit(W, S, NodeSets,
                  Node2Idx->at(W) < Node2Idx->at(V) ? true : HasBackedge))
        F = true;
    }
  }

  if (F)
    unblock(V);
  else {
    for (auto W : AdjK[V]) {
      if (W < S)
        continue;
      if (B[W].count(SV) == 0)
        B[W].insert(SV);
    }
  }
  Stack.pop_back();
  return F;
}

/// Unblock a node in the circuit finding algorithm.
void SwingSchedulerDAG::Circuits::unblock(int U) {
  Blocked.reset(U);
  SmallPtrSet<SUnit *, 4> &BU = B[U];
  while (!BU.empty()) {
    SmallPtrSet<SUnit *, 4>::iterator SI = BU.begin();
    assert(SI != BU.end() && "Invalid B set.");
    SUnit *W = *SI;
    BU.erase(W);
    if (Blocked.test(W->NodeNum))
      unblock(W->NodeNum);
  }
}

/// Identify all the elementary circuits in the dependence graph using
/// Johnson's circuit algorithm.
void SwingSchedulerDAG::findCircuits(NodeSetType &NodeSets) {
  // Swap all the anti dependences in the DAG. That means it is no longer a DAG,
  // but we do this to find the circuits, and then change them back.
  swapAntiDependences(SUnits);

  Circuits Cir(SUnits, Topo);
  // Create the adjacency structure.
  Cir.createAdjacencyStructure(this);
  for (int i = 0, e = SUnits.size(); i != e; ++i) {
    Cir.reset();
    Cir.circuit(i, i, NodeSets);
  }

  // Change the dependences back so that we've created a DAG again.
  swapAntiDependences(SUnits);
}

// Create artificial dependencies between the source of COPY/REG_SEQUENCE that
// is loop-carried to the USE in next iteration. This will help pipeliner avoid
// additional copies that are needed across iterations. An artificial dependence
// edge is added from USE to SOURCE of COPY/REG_SEQUENCE.

// PHI-------Anti-Dep-----> COPY/REG_SEQUENCE (loop-carried)
// SRCOfCopY------True-Dep---> COPY/REG_SEQUENCE
// PHI-------True-Dep------> USEOfPhi

// The mutation creates
// USEOfPHI -------Artificial-Dep---> SRCOfCopy

// This overall will ensure, the USEOfPHI is scheduled before SRCOfCopy
// (since USE is a predecessor), implies, the COPY/ REG_SEQUENCE is scheduled
// late  to avoid additional copies across iterations. The possible scheduling
// order would be
// USEOfPHI --- SRCOfCopy---  COPY/REG_SEQUENCE.

void SwingSchedulerDAG::CopyToPhiMutation::apply(ScheduleDAGInstrs *DAG) {
  for (SUnit &SU : DAG->SUnits) {
    // Find the COPY/REG_SEQUENCE instruction.
    if (!SU.getInstr()->isCopy() && !SU.getInstr()->isRegSequence())
      continue;

    // Record the loop carried PHIs.
    SmallVector<SUnit *, 4> PHISUs;
    // Record the SrcSUs that feed the COPY/REG_SEQUENCE instructions.
    SmallVector<SUnit *, 4> SrcSUs;

    for (auto &Dep : SU.Preds) {
      SUnit *TmpSU = Dep.getSUnit();
      MachineInstr *TmpMI = TmpSU->getInstr();
      SDep::Kind DepKind = Dep.getKind();
      // Save the loop carried PHI.
      if (DepKind == SDep::Anti && TmpMI->isPHI())
        PHISUs.push_back(TmpSU);
      // Save the source of COPY/REG_SEQUENCE.
      // If the source has no pre-decessors, we will end up creating cycles.
      else if (DepKind == SDep::Data && !TmpMI->isPHI() && TmpSU->NumPreds > 0)
        SrcSUs.push_back(TmpSU);
    }

    if (PHISUs.size() == 0 || SrcSUs.size() == 0)
      continue;

    // Find the USEs of PHI. If the use is a PHI or REG_SEQUENCE, push back this
    // SUnit to the container.
    SmallVector<SUnit *, 8> UseSUs;
    for (auto I = PHISUs.begin(); I != PHISUs.end(); ++I) {
      for (auto &Dep : (*I)->Succs) {
        if (Dep.getKind() != SDep::Data)
          continue;

        SUnit *TmpSU = Dep.getSUnit();
        MachineInstr *TmpMI = TmpSU->getInstr();
        if (TmpMI->isPHI() || TmpMI->isRegSequence()) {
          PHISUs.push_back(TmpSU);
          continue;
        }
        UseSUs.push_back(TmpSU);
      }
    }

    if (UseSUs.size() == 0)
      continue;

    SwingSchedulerDAG *SDAG = cast<SwingSchedulerDAG>(DAG);
    // Add the artificial dependencies if it does not form a cycle.
    for (auto I : UseSUs) {
      for (auto Src : SrcSUs) {
        if (!SDAG->Topo.IsReachable(I, Src) && Src != I) {
          Src->addPred(SDep(I, SDep::Artificial));
          SDAG->Topo.AddPred(Src, I);
        }
      }
    }
  }
}

/// Return true for DAG nodes that we ignore when computing the cost functions.
/// We ignore the back-edge recurrence in order to avoid unbounded recursion
/// in the calculation of the ASAP, ALAP, etc functions.
static bool ignoreDependence(const SDep &D, bool isPred) {
  if (D.isArtificial())
    return true;
  return D.getKind() == SDep::Anti && isPred;
}

/// Compute several functions need to order the nodes for scheduling.
///  ASAP - Earliest time to schedule a node.
///  ALAP - Latest time to schedule a node.
///  MOV - Mobility function, difference between ALAP and ASAP.
///  D - Depth of each node.
///  H - Height of each node.
void SwingSchedulerDAG::computeNodeFunctions(NodeSetType &NodeSets) {
  ScheduleInfo.resize(SUnits.size());

  LLVM_DEBUG({
    for (ScheduleDAGTopologicalSort::const_iterator I = Topo.begin(),
                                                    E = Topo.end();
         I != E; ++I) {
      const SUnit &SU = SUnits[*I];
      dumpNode(SU);
    }
  });

  int maxASAP = 0;
  // Compute ASAP and ZeroLatencyDepth.
  for (ScheduleDAGTopologicalSort::const_iterator I = Topo.begin(),
                                                  E = Topo.end();
       I != E; ++I) {
    int asap = 0;
    int zeroLatencyDepth = 0;
    SUnit *SU = &SUnits[*I];
    for (SUnit::const_pred_iterator IP = SU->Preds.begin(),
                                    EP = SU->Preds.end();
         IP != EP; ++IP) {
      SUnit *pred = IP->getSUnit();
      if (IP->getLatency() == 0)
        zeroLatencyDepth =
            std::max(zeroLatencyDepth, getZeroLatencyDepth(pred) + 1);
      if (ignoreDependence(*IP, true))
        continue;
      asap = std::max(asap, (int)(getASAP(pred) + IP->getLatency() -
                                  getDistance(pred, SU, *IP) * MII));
    }
    maxASAP = std::max(maxASAP, asap);
    ScheduleInfo[*I].ASAP = asap;
    ScheduleInfo[*I].ZeroLatencyDepth = zeroLatencyDepth;
  }

  // Compute ALAP, ZeroLatencyHeight, and MOV.
  for (ScheduleDAGTopologicalSort::const_reverse_iterator I = Topo.rbegin(),
                                                          E = Topo.rend();
       I != E; ++I) {
    int alap = maxASAP;
    int zeroLatencyHeight = 0;
    SUnit *SU = &SUnits[*I];
    for (SUnit::const_succ_iterator IS = SU->Succs.begin(),
                                    ES = SU->Succs.end();
         IS != ES; ++IS) {
      SUnit *succ = IS->getSUnit();
      if (IS->getLatency() == 0)
        zeroLatencyHeight =
            std::max(zeroLatencyHeight, getZeroLatencyHeight(succ) + 1);
      if (ignoreDependence(*IS, true))
        continue;
      alap = std::min(alap, (int)(getALAP(succ) - IS->getLatency() +
                                  getDistance(SU, succ, *IS) * MII));
    }

    ScheduleInfo[*I].ALAP = alap;
    ScheduleInfo[*I].ZeroLatencyHeight = zeroLatencyHeight;
  }

  // After computing the node functions, compute the summary for each node set.
  for (NodeSet &I : NodeSets)
    I.computeNodeSetInfo(this);

  LLVM_DEBUG({
    for (unsigned i = 0; i < SUnits.size(); i++) {
      dbgs() << "\tNode " << i << ":\n";
      dbgs() << "\t   ASAP = " << getASAP(&SUnits[i]) << "\n";
      dbgs() << "\t   ALAP = " << getALAP(&SUnits[i]) << "\n";
      dbgs() << "\t   MOV  = " << getMOV(&SUnits[i]) << "\n";
      dbgs() << "\t   D    = " << getDepth(&SUnits[i]) << "\n";
      dbgs() << "\t   H    = " << getHeight(&SUnits[i]) << "\n";
      dbgs() << "\t   ZLD  = " << getZeroLatencyDepth(&SUnits[i]) << "\n";
      dbgs() << "\t   ZLH  = " << getZeroLatencyHeight(&SUnits[i]) << "\n";
    }
  });
}

/// Compute the Pred_L(O) set, as defined in the paper. The set is defined
/// as the predecessors of the elements of NodeOrder that are not also in
/// NodeOrder.
static bool pred_L(SetVector<SUnit *> &NodeOrder,
                   SmallSetVector<SUnit *, 8> &Preds,
                   const NodeSet *S = nullptr) {
  Preds.clear();
  for (SetVector<SUnit *>::iterator I = NodeOrder.begin(), E = NodeOrder.end();
       I != E; ++I) {
    for (SUnit::pred_iterator PI = (*I)->Preds.begin(), PE = (*I)->Preds.end();
         PI != PE; ++PI) {
      if (S && S->count(PI->getSUnit()) == 0)
        continue;
      if (ignoreDependence(*PI, true))
        continue;
      if (NodeOrder.count(PI->getSUnit()) == 0)
        Preds.insert(PI->getSUnit());
    }
    // Back-edges are predecessors with an anti-dependence.
    for (SUnit::const_succ_iterator IS = (*I)->Succs.begin(),
                                    ES = (*I)->Succs.end();
         IS != ES; ++IS) {
      if (IS->getKind() != SDep::Anti)
        continue;
      if (S && S->count(IS->getSUnit()) == 0)
        continue;
      if (NodeOrder.count(IS->getSUnit()) == 0)
        Preds.insert(IS->getSUnit());
    }
  }
  return !Preds.empty();
}

/// Compute the Succ_L(O) set, as defined in the paper. The set is defined
/// as the successors of the elements of NodeOrder that are not also in
/// NodeOrder.
static bool succ_L(SetVector<SUnit *> &NodeOrder,
                   SmallSetVector<SUnit *, 8> &Succs,
                   const NodeSet *S = nullptr) {
  Succs.clear();
  for (SetVector<SUnit *>::iterator I = NodeOrder.begin(), E = NodeOrder.end();
       I != E; ++I) {
    for (SUnit::succ_iterator SI = (*I)->Succs.begin(), SE = (*I)->Succs.end();
         SI != SE; ++SI) {
      if (S && S->count(SI->getSUnit()) == 0)
        continue;
      if (ignoreDependence(*SI, false))
        continue;
      if (NodeOrder.count(SI->getSUnit()) == 0)
        Succs.insert(SI->getSUnit());
    }
    for (SUnit::const_pred_iterator PI = (*I)->Preds.begin(),
                                    PE = (*I)->Preds.end();
         PI != PE; ++PI) {
      if (PI->getKind() != SDep::Anti)
        continue;
      if (S && S->count(PI->getSUnit()) == 0)
        continue;
      if (NodeOrder.count(PI->getSUnit()) == 0)
        Succs.insert(PI->getSUnit());
    }
  }
  return !Succs.empty();
}

/// Return true if there is a path from the specified node to any of the nodes
/// in DestNodes. Keep track and return the nodes in any path.
static bool computePath(SUnit *Cur, SetVector<SUnit *> &Path,
                        SetVector<SUnit *> &DestNodes,
                        SetVector<SUnit *> &Exclude,
                        SmallPtrSet<SUnit *, 8> &Visited) {
  if (Cur->isBoundaryNode())
    return false;
  if (Exclude.count(Cur) != 0)
    return false;
  if (DestNodes.count(Cur) != 0)
    return true;
  if (!Visited.insert(Cur).second)
    return Path.count(Cur) != 0;
  bool FoundPath = false;
  for (auto &SI : Cur->Succs)
    FoundPath |= computePath(SI.getSUnit(), Path, DestNodes, Exclude, Visited);
  for (auto &PI : Cur->Preds)
    if (PI.getKind() == SDep::Anti)
      FoundPath |=
          computePath(PI.getSUnit(), Path, DestNodes, Exclude, Visited);
  if (FoundPath)
    Path.insert(Cur);
  return FoundPath;
}

/// Return true if Set1 is a subset of Set2.
template <class S1Ty, class S2Ty> static bool isSubset(S1Ty &Set1, S2Ty &Set2) {
  for (typename S1Ty::iterator I = Set1.begin(), E = Set1.end(); I != E; ++I)
    if (Set2.count(*I) == 0)
      return false;
  return true;
}

/// Compute the live-out registers for the instructions in a node-set.
/// The live-out registers are those that are defined in the node-set,
/// but not used. Except for use operands of Phis.
static void computeLiveOuts(MachineFunction &MF, RegPressureTracker &RPTracker,
                            NodeSet &NS) {
  const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
  MachineRegisterInfo &MRI = MF.getRegInfo();
  SmallVector<RegisterMaskPair, 8> LiveOutRegs;
  SmallSet<unsigned, 4> Uses;
  for (SUnit *SU : NS) {
    const MachineInstr *MI = SU->getInstr();
    if (MI->isPHI())
      continue;
    for (const MachineOperand &MO : MI->operands())
      if (MO.isReg() && MO.isUse()) {
        Register Reg = MO.getReg();
        if (Register::isVirtualRegister(Reg))
          Uses.insert(Reg);
        else if (MRI.isAllocatable(Reg))
          for (MCRegUnitIterator Units(Reg, TRI); Units.isValid(); ++Units)
            Uses.insert(*Units);
      }
  }
  for (SUnit *SU : NS)
    for (const MachineOperand &MO : SU->getInstr()->operands())
      if (MO.isReg() && MO.isDef() && !MO.isDead()) {
        Register Reg = MO.getReg();
        if (Register::isVirtualRegister(Reg)) {
          if (!Uses.count(Reg))
            LiveOutRegs.push_back(RegisterMaskPair(Reg,
                                                   LaneBitmask::getNone()));
        } else if (MRI.isAllocatable(Reg)) {
          for (MCRegUnitIterator Units(Reg, TRI); Units.isValid(); ++Units)
            if (!Uses.count(*Units))
              LiveOutRegs.push_back(RegisterMaskPair(*Units,
                                                     LaneBitmask::getNone()));
        }
      }
  RPTracker.addLiveRegs(LiveOutRegs);
}

/// A heuristic to filter nodes in recurrent node-sets if the register
/// pressure of a set is too high.
void SwingSchedulerDAG::registerPressureFilter(NodeSetType &NodeSets) {
  for (auto &NS : NodeSets) {
    // Skip small node-sets since they won't cause register pressure problems.
    if (NS.size() <= 2)
      continue;
    IntervalPressure RecRegPressure;
    RegPressureTracker RecRPTracker(RecRegPressure);
    RecRPTracker.init(&MF, &RegClassInfo, &LIS, BB, BB->end(), false, true);
    computeLiveOuts(MF, RecRPTracker, NS);
    RecRPTracker.closeBottom();

    std::vector<SUnit *> SUnits(NS.begin(), NS.end());
    llvm::sort(SUnits, [](const SUnit *A, const SUnit *B) {
      return A->NodeNum > B->NodeNum;
    });

    for (auto &SU : SUnits) {
      // Since we're computing the register pressure for a subset of the
      // instructions in a block, we need to set the tracker for each
      // instruction in the node-set. The tracker is set to the instruction
      // just after the one we're interested in.
      MachineBasicBlock::const_iterator CurInstI = SU->getInstr();
      RecRPTracker.setPos(std::next(CurInstI));

      RegPressureDelta RPDelta;
      ArrayRef<PressureChange> CriticalPSets;
      RecRPTracker.getMaxUpwardPressureDelta(SU->getInstr(), nullptr, RPDelta,
                                             CriticalPSets,
                                             RecRegPressure.MaxSetPressure);
      if (RPDelta.Excess.isValid()) {
        LLVM_DEBUG(
            dbgs() << "Excess register pressure: SU(" << SU->NodeNum << ") "
                   << TRI->getRegPressureSetName(RPDelta.Excess.getPSet())
                   << ":" << RPDelta.Excess.getUnitInc());
        NS.setExceedPressure(SU);
        break;
      }
      RecRPTracker.recede();
    }
  }
}

/// A heuristic to colocate node sets that have the same set of
/// successors.
void SwingSchedulerDAG::colocateNodeSets(NodeSetType &NodeSets) {
  unsigned Colocate = 0;
  for (int i = 0, e = NodeSets.size(); i < e; ++i) {
    NodeSet &N1 = NodeSets[i];
    SmallSetVector<SUnit *, 8> S1;
    if (N1.empty() || !succ_L(N1, S1))
      continue;
    for (int j = i + 1; j < e; ++j) {
      NodeSet &N2 = NodeSets[j];
      if (N1.compareRecMII(N2) != 0)
        continue;
      SmallSetVector<SUnit *, 8> S2;
      if (N2.empty() || !succ_L(N2, S2))
        continue;
      if (isSubset(S1, S2) && S1.size() == S2.size()) {
        N1.setColocate(++Colocate);
        N2.setColocate(Colocate);
        break;
      }
    }
  }
}

/// Check if the existing node-sets are profitable. If not, then ignore the
/// recurrent node-sets, and attempt to schedule all nodes together. This is
/// a heuristic. If the MII is large and all the recurrent node-sets are small,
/// then it's best to try to schedule all instructions together instead of
/// starting with the recurrent node-sets.
void SwingSchedulerDAG::checkNodeSets(NodeSetType &NodeSets) {
  // Look for loops with a large MII.
  if (MII < 17)
    return;
  // Check if the node-set contains only a simple add recurrence.
  for (auto &NS : NodeSets) {
    if (NS.getRecMII() > 2)
      return;
    if (NS.getMaxDepth() > MII)
      return;
  }
  NodeSets.clear();
  LLVM_DEBUG(dbgs() << "Clear recurrence node-sets\n");
  return;
}

/// Add the nodes that do not belong to a recurrence set into groups
/// based upon connected componenets.
void SwingSchedulerDAG::groupRemainingNodes(NodeSetType &NodeSets) {
  SetVector<SUnit *> NodesAdded;
  SmallPtrSet<SUnit *, 8> Visited;
  // Add the nodes that are on a path between the previous node sets and
  // the current node set.
  for (NodeSet &I : NodeSets) {
    SmallSetVector<SUnit *, 8> N;
    // Add the nodes from the current node set to the previous node set.
    if (succ_L(I, N)) {
      SetVector<SUnit *> Path;
      for (SUnit *NI : N) {
        Visited.clear();
        computePath(NI, Path, NodesAdded, I, Visited);
      }
      if (!Path.empty())
        I.insert(Path.begin(), Path.end());
    }
    // Add the nodes from the previous node set to the current node set.
    N.clear();
    if (succ_L(NodesAdded, N)) {
      SetVector<SUnit *> Path;
      for (SUnit *NI : N) {
        Visited.clear();
        computePath(NI, Path, I, NodesAdded, Visited);
      }
      if (!Path.empty())
        I.insert(Path.begin(), Path.end());
    }
    NodesAdded.insert(I.begin(), I.end());
  }

  // Create a new node set with the connected nodes of any successor of a node
  // in a recurrent set.
  NodeSet NewSet;
  SmallSetVector<SUnit *, 8> N;
  if (succ_L(NodesAdded, N))
    for (SUnit *I : N)
      addConnectedNodes(I, NewSet, NodesAdded);
  if (!NewSet.empty())
    NodeSets.push_back(NewSet);

  // Create a new node set with the connected nodes of any predecessor of a node
  // in a recurrent set.
  NewSet.clear();
  if (pred_L(NodesAdded, N))
    for (SUnit *I : N)
      addConnectedNodes(I, NewSet, NodesAdded);
  if (!NewSet.empty())
    NodeSets.push_back(NewSet);

  // Create new nodes sets with the connected nodes any remaining node that
  // has no predecessor.
  for (unsigned i = 0; i < SUnits.size(); ++i) {
    SUnit *SU = &SUnits[i];
    if (NodesAdded.count(SU) == 0) {
      NewSet.clear();
      addConnectedNodes(SU, NewSet, NodesAdded);
      if (!NewSet.empty())
        NodeSets.push_back(NewSet);
    }
  }
}

/// Add the node to the set, and add all of its connected nodes to the set.
void SwingSchedulerDAG::addConnectedNodes(SUnit *SU, NodeSet &NewSet,
                                          SetVector<SUnit *> &NodesAdded) {
  NewSet.insert(SU);
  NodesAdded.insert(SU);
  for (auto &SI : SU->Succs) {
    SUnit *Successor = SI.getSUnit();
    if (!SI.isArtificial() && NodesAdded.count(Successor) == 0)
      addConnectedNodes(Successor, NewSet, NodesAdded);
  }
  for (auto &PI : SU->Preds) {
    SUnit *Predecessor = PI.getSUnit();
    if (!PI.isArtificial() && NodesAdded.count(Predecessor) == 0)
      addConnectedNodes(Predecessor, NewSet, NodesAdded);
  }
}

/// Return true if Set1 contains elements in Set2. The elements in common
/// are returned in a different container.
static bool isIntersect(SmallSetVector<SUnit *, 8> &Set1, const NodeSet &Set2,
                        SmallSetVector<SUnit *, 8> &Result) {
  Result.clear();
  for (unsigned i = 0, e = Set1.size(); i != e; ++i) {
    SUnit *SU = Set1[i];
    if (Set2.count(SU) != 0)
      Result.insert(SU);
  }
  return !Result.empty();
}

/// Merge the recurrence node sets that have the same initial node.
void SwingSchedulerDAG::fuseRecs(NodeSetType &NodeSets) {
  for (NodeSetType::iterator I = NodeSets.begin(), E = NodeSets.end(); I != E;
       ++I) {
    NodeSet &NI = *I;
    for (NodeSetType::iterator J = I + 1; J != E;) {
      NodeSet &NJ = *J;
      if (NI.getNode(0)->NodeNum == NJ.getNode(0)->NodeNum) {
        if (NJ.compareRecMII(NI) > 0)
          NI.setRecMII(NJ.getRecMII());
        for (NodeSet::iterator NII = J->begin(), ENI = J->end(); NII != ENI;
             ++NII)
          I->insert(*NII);
        NodeSets.erase(J);
        E = NodeSets.end();
      } else {
        ++J;
      }
    }
  }
}

/// Remove nodes that have been scheduled in previous NodeSets.
void SwingSchedulerDAG::removeDuplicateNodes(NodeSetType &NodeSets) {
  for (NodeSetType::iterator I = NodeSets.begin(), E = NodeSets.end(); I != E;
       ++I)
    for (NodeSetType::iterator J = I + 1; J != E;) {
      J->remove_if([&](SUnit *SUJ) { return I->count(SUJ); });

      if (J->empty()) {
        NodeSets.erase(J);
        E = NodeSets.end();
      } else {
        ++J;
      }
    }
}

/// Compute an ordered list of the dependence graph nodes, which
/// indicates the order that the nodes will be scheduled.  This is a
/// two-level algorithm. First, a partial order is created, which
/// consists of a list of sets ordered from highest to lowest priority.
void SwingSchedulerDAG::computeNodeOrder(NodeSetType &NodeSets) {
  SmallSetVector<SUnit *, 8> R;
  NodeOrder.clear();

  for (auto &Nodes : NodeSets) {
    LLVM_DEBUG(dbgs() << "NodeSet size " << Nodes.size() << "\n");
    OrderKind Order;
    SmallSetVector<SUnit *, 8> N;
    if (pred_L(NodeOrder, N) && isSubset(N, Nodes)) {
      R.insert(N.begin(), N.end());
      Order = BottomUp;
      LLVM_DEBUG(dbgs() << "  Bottom up (preds) ");
    } else if (succ_L(NodeOrder, N) && isSubset(N, Nodes)) {
      R.insert(N.begin(), N.end());
      Order = TopDown;
      LLVM_DEBUG(dbgs() << "  Top down (succs) ");
    } else if (isIntersect(N, Nodes, R)) {
      // If some of the successors are in the existing node-set, then use the
      // top-down ordering.
      Order = TopDown;
      LLVM_DEBUG(dbgs() << "  Top down (intersect) ");
    } else if (NodeSets.size() == 1) {
      for (auto &N : Nodes)
        if (N->Succs.size() == 0)
          R.insert(N);
      Order = BottomUp;
      LLVM_DEBUG(dbgs() << "  Bottom up (all) ");
    } else {
      // Find the node with the highest ASAP.
      SUnit *maxASAP = nullptr;
      for (SUnit *SU : Nodes) {
        if (maxASAP == nullptr || getASAP(SU) > getASAP(maxASAP) ||
            (getASAP(SU) == getASAP(maxASAP) && SU->NodeNum > maxASAP->NodeNum))
          maxASAP = SU;
      }
      R.insert(maxASAP);
      Order = BottomUp;
      LLVM_DEBUG(dbgs() << "  Bottom up (default) ");
    }

    while (!R.empty()) {
      if (Order == TopDown) {
        // Choose the node with the maximum height.  If more than one, choose
        // the node wiTH the maximum ZeroLatencyHeight. If still more than one,
        // choose the node with the lowest MOV.
        while (!R.empty()) {
          SUnit *maxHeight = nullptr;
          for (SUnit *I : R) {
            if (maxHeight == nullptr || getHeight(I) > getHeight(maxHeight))
              maxHeight = I;
            else if (getHeight(I) == getHeight(maxHeight) &&
                     getZeroLatencyHeight(I) > getZeroLatencyHeight(maxHeight))
              maxHeight = I;
            else if (getHeight(I) == getHeight(maxHeight) &&
                     getZeroLatencyHeight(I) ==
                         getZeroLatencyHeight(maxHeight) &&
                     getMOV(I) < getMOV(maxHeight))
              maxHeight = I;
          }
          NodeOrder.insert(maxHeight);
          LLVM_DEBUG(dbgs() << maxHeight->NodeNum << " ");
          R.remove(maxHeight);
          for (const auto &I : maxHeight->Succs) {
            if (Nodes.count(I.getSUnit()) == 0)
              continue;
            if (NodeOrder.count(I.getSUnit()) != 0)
              continue;
            if (ignoreDependence(I, false))
              continue;
            R.insert(I.getSUnit());
          }
          // Back-edges are predecessors with an anti-dependence.
          for (const auto &I : maxHeight->Preds) {
            if (I.getKind() != SDep::Anti)
              continue;
            if (Nodes.count(I.getSUnit()) == 0)
              continue;
            if (NodeOrder.count(I.getSUnit()) != 0)
              continue;
            R.insert(I.getSUnit());
          }
        }
        Order = BottomUp;
        LLVM_DEBUG(dbgs() << "\n   Switching order to bottom up ");
        SmallSetVector<SUnit *, 8> N;
        if (pred_L(NodeOrder, N, &Nodes))
          R.insert(N.begin(), N.end());
      } else {
        // Choose the node with the maximum depth.  If more than one, choose
        // the node with the maximum ZeroLatencyDepth. If still more than one,
        // choose the node with the lowest MOV.
        while (!R.empty()) {
          SUnit *maxDepth = nullptr;
          for (SUnit *I : R) {
            if (maxDepth == nullptr || getDepth(I) > getDepth(maxDepth))
              maxDepth = I;
            else if (getDepth(I) == getDepth(maxDepth) &&
                     getZeroLatencyDepth(I) > getZeroLatencyDepth(maxDepth))
              maxDepth = I;
            else if (getDepth(I) == getDepth(maxDepth) &&
                     getZeroLatencyDepth(I) == getZeroLatencyDepth(maxDepth) &&
                     getMOV(I) < getMOV(maxDepth))
              maxDepth = I;
          }
          NodeOrder.insert(maxDepth);
          LLVM_DEBUG(dbgs() << maxDepth->NodeNum << " ");
          R.remove(maxDepth);
          if (Nodes.isExceedSU(maxDepth)) {
            Order = TopDown;
            R.clear();
            R.insert(Nodes.getNode(0));
            break;
          }
          for (const auto &I : maxDepth->Preds) {
            if (Nodes.count(I.getSUnit()) == 0)
              continue;
            if (NodeOrder.count(I.getSUnit()) != 0)
              continue;
            R.insert(I.getSUnit());
          }
          // Back-edges are predecessors with an anti-dependence.
          for (const auto &I : maxDepth->Succs) {
            if (I.getKind() != SDep::Anti)
              continue;
            if (Nodes.count(I.getSUnit()) == 0)
              continue;
            if (NodeOrder.count(I.getSUnit()) != 0)
              continue;
            R.insert(I.getSUnit());
          }
        }
        Order = TopDown;
        LLVM_DEBUG(dbgs() << "\n   Switching order to top down ");
        SmallSetVector<SUnit *, 8> N;
        if (succ_L(NodeOrder, N, &Nodes))
          R.insert(N.begin(), N.end());
      }
    }
    LLVM_DEBUG(dbgs() << "\nDone with Nodeset\n");
  }

  LLVM_DEBUG({
    dbgs() << "Node order: ";
    for (SUnit *I : NodeOrder)
      dbgs() << " " << I->NodeNum << " ";
    dbgs() << "\n";
  });
}

/// Process the nodes in the computed order and create the pipelined schedule
/// of the instructions, if possible. Return true if a schedule is found.
bool SwingSchedulerDAG::schedulePipeline(SMSchedule &Schedule) {

  if (NodeOrder.empty()){
    LLVM_DEBUG(dbgs() << "NodeOrder is empty! abort scheduling\n" );
    return false;
  }

  bool scheduleFound = false;
  unsigned II = 0;
  // Keep increasing II until a valid schedule is found.
  for (II = MII; II <= MAX_II && !scheduleFound; ++II) {
    Schedule.reset();
    Schedule.setInitiationInterval(II);
    LLVM_DEBUG(dbgs() << "Try to schedule with " << II << "\n");

    SetVector<SUnit *>::iterator NI = NodeOrder.begin();
    SetVector<SUnit *>::iterator NE = NodeOrder.end();
    do {
      SUnit *SU = *NI;

      // Compute the schedule time for the instruction, which is based
      // upon the scheduled time for any predecessors/successors.
      int EarlyStart = INT_MIN;
      int LateStart = INT_MAX;
      // These values are set when the size of the schedule window is limited
      // due to chain dependences.
      int SchedEnd = INT_MAX;
      int SchedStart = INT_MIN;
      Schedule.computeStart(SU, &EarlyStart, &LateStart, &SchedEnd, &SchedStart,
                            II, this);
      LLVM_DEBUG({
        dbgs() << "\n";
        dbgs() << "Inst (" << SU->NodeNum << ") ";
        SU->getInstr()->dump();
        dbgs() << "\n";
      });
      LLVM_DEBUG({
        dbgs() << format("\tes: %8x ls: %8x me: %8x ms: %8x\n", EarlyStart,
                         LateStart, SchedEnd, SchedStart);
      });

      if (EarlyStart > LateStart || SchedEnd < EarlyStart ||
          SchedStart > LateStart)
        scheduleFound = false;
      else if (EarlyStart != INT_MIN && LateStart == INT_MAX) {
        SchedEnd = std::min(SchedEnd, EarlyStart + (int)II - 1);
        scheduleFound = Schedule.insert(SU, EarlyStart, SchedEnd, II);
      } else if (EarlyStart == INT_MIN && LateStart != INT_MAX) {
        SchedStart = std::max(SchedStart, LateStart - (int)II + 1);
        scheduleFound = Schedule.insert(SU, LateStart, SchedStart, II);
      } else if (EarlyStart != INT_MIN && LateStart != INT_MAX) {
        SchedEnd =
            std::min(SchedEnd, std::min(LateStart, EarlyStart + (int)II - 1));
        // When scheduling a Phi it is better to start at the late cycle and go
        // backwards. The default order may insert the Phi too far away from
        // its first dependence.
        if (SU->getInstr()->isPHI())
          scheduleFound = Schedule.insert(SU, SchedEnd, EarlyStart, II);
        else
          scheduleFound = Schedule.insert(SU, EarlyStart, SchedEnd, II);
      } else {
        int FirstCycle = Schedule.getFirstCycle();
        scheduleFound = Schedule.insert(SU, FirstCycle + getASAP(SU),
                                        FirstCycle + getASAP(SU) + II - 1, II);
      }
      // Even if we find a schedule, make sure the schedule doesn't exceed the
      // allowable number of stages. We keep trying if this happens.
      if (scheduleFound)
        if (SwpMaxStages > -1 &&
            Schedule.getMaxStageCount() > (unsigned)SwpMaxStages)
          scheduleFound = false;

      LLVM_DEBUG({
        if (!scheduleFound)
          dbgs() << "\tCan't schedule\n";
      });
    } while (++NI != NE && scheduleFound);

    // If a schedule is found, check if it is a valid schedule too.
    if (scheduleFound)
      scheduleFound = Schedule.isValidSchedule(this);
  }

  LLVM_DEBUG(dbgs() << "Schedule Found? " << scheduleFound << " (II=" << II
                    << ")\n");

  if (scheduleFound)
    Schedule.finalizeSchedule(this);
  else
    Schedule.reset();

  return scheduleFound && Schedule.getMaxStageCount() > 0;
}

/// Return true if we can compute the amount the instruction changes
/// during each iteration. Set Delta to the amount of the change.
bool SwingSchedulerDAG::computeDelta(MachineInstr &MI, unsigned &Delta) {
  const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
  const MachineOperand *BaseOp;
  int64_t Offset;
  if (!TII->getMemOperandWithOffset(MI, BaseOp, Offset, TRI))
    return false;

  if (!BaseOp->isReg())
    return false;

  Register BaseReg = BaseOp->getReg();

  MachineRegisterInfo &MRI = MF.getRegInfo();
  // Check if there is a Phi. If so, get the definition in the loop.
  MachineInstr *BaseDef = MRI.getVRegDef(BaseReg);
  if (BaseDef && BaseDef->isPHI()) {
    BaseReg = getLoopPhiReg(*BaseDef, MI.getParent());
    BaseDef = MRI.getVRegDef(BaseReg);
  }
  if (!BaseDef)
    return false;

  int D = 0;
  if (!TII->getIncrementValue(*BaseDef, D) && D >= 0)
    return false;

  Delta = D;
  return true;
}

/// Check if we can change the instruction to use an offset value from the
/// previous iteration. If so, return true and set the base and offset values
/// so that we can rewrite the load, if necessary.
///   v1 = Phi(v0, v3)
///   v2 = load v1, 0
///   v3 = post_store v1, 4, x
/// This function enables the load to be rewritten as v2 = load v3, 4.
bool SwingSchedulerDAG::canUseLastOffsetValue(MachineInstr *MI,
                                              unsigned &BasePos,
                                              unsigned &OffsetPos,
                                              unsigned &NewBase,
                                              int64_t &Offset) {
  // Get the load instruction.
  if (TII->isPostIncrement(*MI))
    return false;
  unsigned BasePosLd, OffsetPosLd;
  if (!TII->getBaseAndOffsetPosition(*MI, BasePosLd, OffsetPosLd))
    return false;
  Register BaseReg = MI->getOperand(BasePosLd).getReg();

  // Look for the Phi instruction.
  MachineRegisterInfo &MRI = MI->getMF()->getRegInfo();
  MachineInstr *Phi = MRI.getVRegDef(BaseReg);
  if (!Phi || !Phi->isPHI())
    return false;
  // Get the register defined in the loop block.
  unsigned PrevReg = getLoopPhiReg(*Phi, MI->getParent());
  if (!PrevReg)
    return false;

  // Check for the post-increment load/store instruction.
  MachineInstr *PrevDef = MRI.getVRegDef(PrevReg);
  if (!PrevDef || PrevDef == MI)
    return false;

  if (!TII->isPostIncrement(*PrevDef))
    return false;

  unsigned BasePos1 = 0, OffsetPos1 = 0;
  if (!TII->getBaseAndOffsetPosition(*PrevDef, BasePos1, OffsetPos1))
    return false;

  // Make sure that the instructions do not access the same memory location in
  // the next iteration.
  int64_t LoadOffset = MI->getOperand(OffsetPosLd).getImm();
  int64_t StoreOffset = PrevDef->getOperand(OffsetPos1).getImm();
  MachineInstr *NewMI = MF.CloneMachineInstr(MI);
  NewMI->getOperand(OffsetPosLd).setImm(LoadOffset + StoreOffset);
  bool Disjoint = TII->areMemAccessesTriviallyDisjoint(*NewMI, *PrevDef);
  MF.DeleteMachineInstr(NewMI);
  if (!Disjoint)
    return false;

  // Set the return value once we determine that we return true.
  BasePos = BasePosLd;
  OffsetPos = OffsetPosLd;
  NewBase = PrevReg;
  Offset = StoreOffset;
  return true;
}

/// Apply changes to the instruction if needed. The changes are need
/// to improve the scheduling and depend up on the final schedule.
void SwingSchedulerDAG::applyInstrChange(MachineInstr *MI,
                                         SMSchedule &Schedule) {
  SUnit *SU = getSUnit(MI);
  DenseMap<SUnit *, std::pair<unsigned, int64_t>>::iterator It =
      InstrChanges.find(SU);
  if (It != InstrChanges.end()) {
    std::pair<unsigned, int64_t> RegAndOffset = It->second;
    unsigned BasePos, OffsetPos;
    if (!TII->getBaseAndOffsetPosition(*MI, BasePos, OffsetPos))
      return;
    Register BaseReg = MI->getOperand(BasePos).getReg();
    MachineInstr *LoopDef = findDefInLoop(BaseReg);
    int DefStageNum = Schedule.stageScheduled(getSUnit(LoopDef));
    int DefCycleNum = Schedule.cycleScheduled(getSUnit(LoopDef));
    int BaseStageNum = Schedule.stageScheduled(SU);
    int BaseCycleNum = Schedule.cycleScheduled(SU);
    if (BaseStageNum < DefStageNum) {
      MachineInstr *NewMI = MF.CloneMachineInstr(MI);
      int OffsetDiff = DefStageNum - BaseStageNum;
      if (DefCycleNum < BaseCycleNum) {
        NewMI->getOperand(BasePos).setReg(RegAndOffset.first);
        if (OffsetDiff > 0)
          --OffsetDiff;
      }
      int64_t NewOffset =
          MI->getOperand(OffsetPos).getImm() + RegAndOffset.second * OffsetDiff;
      NewMI->getOperand(OffsetPos).setImm(NewOffset);
      SU->setInstr(NewMI);
      MISUnitMap[NewMI] = SU;
      NewMIs[MI] = NewMI;
    }
  }
}

/// Return the instruction in the loop that defines the register.
/// If the definition is a Phi, then follow the Phi operand to
/// the instruction in the loop.
MachineInstr *SwingSchedulerDAG::findDefInLoop(unsigned Reg) {
  SmallPtrSet<MachineInstr *, 8> Visited;
  MachineInstr *Def = MRI.getVRegDef(Reg);
  while (Def->isPHI()) {
    if (!Visited.insert(Def).second)
      break;
    for (unsigned i = 1, e = Def->getNumOperands(); i < e; i += 2)
      if (Def->getOperand(i + 1).getMBB() == BB) {
        Def = MRI.getVRegDef(Def->getOperand(i).getReg());
        break;
      }
  }
  return Def;
}

/// Return true for an order or output dependence that is loop carried
/// potentially. A dependence is loop carried if the destination defines a valu
/// that may be used or defined by the source in a subsequent iteration.
bool SwingSchedulerDAG::isLoopCarriedDep(SUnit *Source, const SDep &Dep,
                                         bool isSucc) {
  if ((Dep.getKind() != SDep::Order && Dep.getKind() != SDep::Output) ||
      Dep.isArtificial())
    return false;

  if (!SwpPruneLoopCarried)
    return true;

  if (Dep.getKind() == SDep::Output)
    return true;

  MachineInstr *SI = Source->getInstr();
  MachineInstr *DI = Dep.getSUnit()->getInstr();
  if (!isSucc)
    std::swap(SI, DI);
  assert(SI != nullptr && DI != nullptr && "Expecting SUnit with an MI.");

  // Assume ordered loads and stores may have a loop carried dependence.
  if (SI->hasUnmodeledSideEffects() || DI->hasUnmodeledSideEffects() ||
      SI->mayRaiseFPException() || DI->mayRaiseFPException() ||
      SI->hasOrderedMemoryRef() || DI->hasOrderedMemoryRef())
    return true;

  // Only chain dependences between a load and store can be loop carried.
  if (!DI->mayStore() || !SI->mayLoad())
    return false;

  unsigned DeltaS, DeltaD;
  if (!computeDelta(*SI, DeltaS) || !computeDelta(*DI, DeltaD))
    return true;

  const MachineOperand *BaseOpS, *BaseOpD;
  int64_t OffsetS, OffsetD;
  const TargetRegisterInfo *TRI = MF.getSubtarget().getRegisterInfo();
  if (!TII->getMemOperandWithOffset(*SI, BaseOpS, OffsetS, TRI) ||
      !TII->getMemOperandWithOffset(*DI, BaseOpD, OffsetD, TRI))
    return true;

  if (!BaseOpS->isIdenticalTo(*BaseOpD))
    return true;

  // Check that the base register is incremented by a constant value for each
  // iteration.
  MachineInstr *Def = MRI.getVRegDef(BaseOpS->getReg());
  if (!Def || !Def->isPHI())
    return true;
  unsigned InitVal = 0;
  unsigned LoopVal = 0;
  getPhiRegs(*Def, BB, InitVal, LoopVal);
  MachineInstr *LoopDef = MRI.getVRegDef(LoopVal);
  int D = 0;
  if (!LoopDef || !TII->getIncrementValue(*LoopDef, D))
    return true;

  uint64_t AccessSizeS = (*SI->memoperands_begin())->getSize();
  uint64_t AccessSizeD = (*DI->memoperands_begin())->getSize();

  // This is the main test, which checks the offset values and the loop
  // increment value to determine if the accesses may be loop carried.
  if (AccessSizeS == MemoryLocation::UnknownSize ||
      AccessSizeD == MemoryLocation::UnknownSize)
    return true;

  if (DeltaS != DeltaD || DeltaS < AccessSizeS || DeltaD < AccessSizeD)
    return true;

  return (OffsetS + (int64_t)AccessSizeS < OffsetD + (int64_t)AccessSizeD);
}

void SwingSchedulerDAG::postprocessDAG() {
  for (auto &M : Mutations)
    M->apply(this);
}

/// Try to schedule the node at the specified StartCycle and continue
/// until the node is schedule or the EndCycle is reached.  This function
/// returns true if the node is scheduled.  This routine may search either
/// forward or backward for a place to insert the instruction based upon
/// the relative values of StartCycle and EndCycle.
bool SMSchedule::insert(SUnit *SU, int StartCycle, int EndCycle, int II) {
  bool forward = true;
  LLVM_DEBUG({
    dbgs() << "Trying to insert node between " << StartCycle << " and "
           << EndCycle << " II: " << II << "\n";
  });
  if (StartCycle > EndCycle)
    forward = false;

  // The terminating condition depends on the direction.
  int termCycle = forward ? EndCycle + 1 : EndCycle - 1;
  for (int curCycle = StartCycle; curCycle != termCycle;
       forward ? ++curCycle : --curCycle) {

    // Add the already scheduled instructions at the specified cycle to the
    // DFA.
    ProcItinResources.clearResources();
    for (int checkCycle = FirstCycle + ((curCycle - FirstCycle) % II);
         checkCycle <= LastCycle; checkCycle += II) {
      std::deque<SUnit *> &cycleInstrs = ScheduledInstrs[checkCycle];

      for (std::deque<SUnit *>::iterator I = cycleInstrs.begin(),
                                         E = cycleInstrs.end();
           I != E; ++I) {
        if (ST.getInstrInfo()->isZeroCost((*I)->getInstr()->getOpcode()))
          continue;
        assert(ProcItinResources.canReserveResources(*(*I)->getInstr()) &&
               "These instructions have already been scheduled.");
        ProcItinResources.reserveResources(*(*I)->getInstr());
      }
    }
    if (ST.getInstrInfo()->isZeroCost(SU->getInstr()->getOpcode()) ||
        ProcItinResources.canReserveResources(*SU->getInstr())) {
      LLVM_DEBUG({
        dbgs() << "\tinsert at cycle " << curCycle << " ";
        SU->getInstr()->dump();
      });

      ScheduledInstrs[curCycle].push_back(SU);
      InstrToCycle.insert(std::make_pair(SU, curCycle));
      if (curCycle > LastCycle)
        LastCycle = curCycle;
      if (curCycle < FirstCycle)
        FirstCycle = curCycle;
      return true;
    }
    LLVM_DEBUG({
      dbgs() << "\tfailed to insert at cycle " << curCycle << " ";
      SU->getInstr()->dump();
    });
  }
  return false;
}

// Return the cycle of the earliest scheduled instruction in the chain.
int SMSchedule::earliestCycleInChain(const SDep &Dep) {
  SmallPtrSet<SUnit *, 8> Visited;
  SmallVector<SDep, 8> Worklist;
  Worklist.push_back(Dep);
  int EarlyCycle = INT_MAX;
  while (!Worklist.empty()) {
    const SDep &Cur = Worklist.pop_back_val();
    SUnit *PrevSU = Cur.getSUnit();
    if (Visited.count(PrevSU))
      continue;
    std::map<SUnit *, int>::const_iterator it = InstrToCycle.find(PrevSU);
    if (it == InstrToCycle.end())
      continue;
    EarlyCycle = std::min(EarlyCycle, it->second);
    for (const auto &PI : PrevSU->Preds)
      if (PI.getKind() == SDep::Order || Dep.getKind() == SDep::Output)
        Worklist.push_back(PI);
    Visited.insert(PrevSU);
  }
  return EarlyCycle;
}

// Return the cycle of the latest scheduled instruction in the chain.
int SMSchedule::latestCycleInChain(const SDep &Dep) {
  SmallPtrSet<SUnit *, 8> Visited;
  SmallVector<SDep, 8> Worklist;
  Worklist.push_back(Dep);
  int LateCycle = INT_MIN;
  while (!Worklist.empty()) {
    const SDep &Cur = Worklist.pop_back_val();
    SUnit *SuccSU = Cur.getSUnit();
    if (Visited.count(SuccSU))
      continue;
    std::map<SUnit *, int>::const_iterator it = InstrToCycle.find(SuccSU);
    if (it == InstrToCycle.end())
      continue;
    LateCycle = std::max(LateCycle, it->second);
    for (const auto &SI : SuccSU->Succs)
      if (SI.getKind() == SDep::Order || Dep.getKind() == SDep::Output)
        Worklist.push_back(SI);
    Visited.insert(SuccSU);
  }
  return LateCycle;
}

/// If an instruction has a use that spans multiple iterations, then
/// return true. These instructions are characterized by having a back-ege
/// to a Phi, which contains a reference to another Phi.
static SUnit *multipleIterations(SUnit *SU, SwingSchedulerDAG *DAG) {
  for (auto &P : SU->Preds)
    if (DAG->isBackedge(SU, P) && P.getSUnit()->getInstr()->isPHI())
      for (auto &S : P.getSUnit()->Succs)
        if (S.getKind() == SDep::Data && S.getSUnit()->getInstr()->isPHI())
          return P.getSUnit();
  return nullptr;
}

/// Compute the scheduling start slot for the instruction.  The start slot
/// depends on any predecessor or successor nodes scheduled already.
void SMSchedule::computeStart(SUnit *SU, int *MaxEarlyStart, int *MinLateStart,
                              int *MinEnd, int *MaxStart, int II,
                              SwingSchedulerDAG *DAG) {
  // Iterate over each instruction that has been scheduled already.  The start
  // slot computation depends on whether the previously scheduled instruction
  // is a predecessor or successor of the specified instruction.
  for (int cycle = getFirstCycle(); cycle <= LastCycle; ++cycle) {

    // Iterate over each instruction in the current cycle.
    for (SUnit *I : getInstructions(cycle)) {
      // Because we're processing a DAG for the dependences, we recognize
      // the back-edge in recurrences by anti dependences.
      for (unsigned i = 0, e = (unsigned)SU->Preds.size(); i != e; ++i) {
        const SDep &Dep = SU->Preds[i];
        if (Dep.getSUnit() == I) {
          if (!DAG->isBackedge(SU, Dep)) {
            int EarlyStart = cycle + Dep.getLatency() -
                             DAG->getDistance(Dep.getSUnit(), SU, Dep) * II;
            *MaxEarlyStart = std::max(*MaxEarlyStart, EarlyStart);
            if (DAG->isLoopCarriedDep(SU, Dep, false)) {
              int End = earliestCycleInChain(Dep) + (II - 1);
              *MinEnd = std::min(*MinEnd, End);
            }
          } else {
            int LateStart = cycle - Dep.getLatency() +
                            DAG->getDistance(SU, Dep.getSUnit(), Dep) * II;
            *MinLateStart = std::min(*MinLateStart, LateStart);
          }
        }
        // For instruction that requires multiple iterations, make sure that
        // the dependent instruction is not scheduled past the definition.
        SUnit *BE = multipleIterations(I, DAG);
        if (BE && Dep.getSUnit() == BE && !SU->getInstr()->isPHI() &&
            !SU->isPred(I))
          *MinLateStart = std::min(*MinLateStart, cycle);
      }
      for (unsigned i = 0, e = (unsigned)SU->Succs.size(); i != e; ++i) {
        if (SU->Succs[i].getSUnit() == I) {
          const SDep &Dep = SU->Succs[i];
          if (!DAG->isBackedge(SU, Dep)) {
            int LateStart = cycle - Dep.getLatency() +
                            DAG->getDistance(SU, Dep.getSUnit(), Dep) * II;
            *MinLateStart = std::min(*MinLateStart, LateStart);
            if (DAG->isLoopCarriedDep(SU, Dep)) {
              int Start = latestCycleInChain(Dep) + 1 - II;
              *MaxStart = std::max(*MaxStart, Start);
            }
          } else {
            int EarlyStart = cycle + Dep.getLatency() -
                             DAG->getDistance(Dep.getSUnit(), SU, Dep) * II;
            *MaxEarlyStart = std::max(*MaxEarlyStart, EarlyStart);
          }
        }
      }
    }
  }
}

/// Order the instructions within a cycle so that the definitions occur
/// before the uses. Returns true if the instruction is added to the start
/// of the list, or false if added to the end.
void SMSchedule::orderDependence(SwingSchedulerDAG *SSD, SUnit *SU,
                                 std::deque<SUnit *> &Insts) {
  MachineInstr *MI = SU->getInstr();
  bool OrderBeforeUse = false;
  bool OrderAfterDef = false;
  bool OrderBeforeDef = false;
  unsigned MoveDef = 0;
  unsigned MoveUse = 0;
  int StageInst1 = stageScheduled(SU);

  unsigned Pos = 0;
  for (std::deque<SUnit *>::iterator I = Insts.begin(), E = Insts.end(); I != E;
       ++I, ++Pos) {
    for (unsigned i = 0, e = MI->getNumOperands(); i < e; ++i) {
      MachineOperand &MO = MI->getOperand(i);
      if (!MO.isReg() || !Register::isVirtualRegister(MO.getReg()))
        continue;

      Register Reg = MO.getReg();
      unsigned BasePos, OffsetPos;
      if (ST.getInstrInfo()->getBaseAndOffsetPosition(*MI, BasePos, OffsetPos))
        if (MI->getOperand(BasePos).getReg() == Reg)
          if (unsigned NewReg = SSD->getInstrBaseReg(SU))
            Reg = NewReg;
      bool Reads, Writes;
      std::tie(Reads, Writes) =
          (*I)->getInstr()->readsWritesVirtualRegister(Reg);
      if (MO.isDef() && Reads && stageScheduled(*I) <= StageInst1) {
        OrderBeforeUse = true;
        if (MoveUse == 0)
          MoveUse = Pos;
      } else if (MO.isDef() && Reads && stageScheduled(*I) > StageInst1) {
        // Add the instruction after the scheduled instruction.
        OrderAfterDef = true;
        MoveDef = Pos;
      } else if (MO.isUse() && Writes && stageScheduled(*I) == StageInst1) {
        if (cycleScheduled(*I) == cycleScheduled(SU) && !(*I)->isSucc(SU)) {
          OrderBeforeUse = true;
          if (MoveUse == 0)
            MoveUse = Pos;
        } else {
          OrderAfterDef = true;
          MoveDef = Pos;
        }
      } else if (MO.isUse() && Writes && stageScheduled(*I) > StageInst1) {
        OrderBeforeUse = true;
        if (MoveUse == 0)
          MoveUse = Pos;
        if (MoveUse != 0) {
          OrderAfterDef = true;
          MoveDef = Pos - 1;
        }
      } else if (MO.isUse() && Writes && stageScheduled(*I) < StageInst1) {
        // Add the instruction before the scheduled instruction.
        OrderBeforeUse = true;
        if (MoveUse == 0)
          MoveUse = Pos;
      } else if (MO.isUse() && stageScheduled(*I) == StageInst1 &&
                 isLoopCarriedDefOfUse(SSD, (*I)->getInstr(), MO)) {
        if (MoveUse == 0) {
          OrderBeforeDef = true;
          MoveUse = Pos;
        }
      }
    }
    // Check for order dependences between instructions. Make sure the source
    // is ordered before the destination.
    for (auto &S : SU->Succs) {
      if (S.getSUnit() != *I)
        continue;
      if (S.getKind() == SDep::Order && stageScheduled(*I) == StageInst1) {
        OrderBeforeUse = true;
        if (Pos < MoveUse)
          MoveUse = Pos;
      }
      // We did not handle HW dependences in previous for loop,
      // and we normally set Latency = 0 for Anti deps,
      // so may have nodes in same cycle with Anti denpendent on HW regs.
      else if (S.getKind() == SDep::Anti && stageScheduled(*I) == StageInst1) {
        OrderBeforeUse = true;
        if ((MoveUse == 0) || (Pos < MoveUse))
          MoveUse = Pos;
      }
    }
    for (auto &P : SU->Preds) {
      if (P.getSUnit() != *I)
        continue;
      if (P.getKind() == SDep::Order && stageScheduled(*I) == StageInst1) {
        OrderAfterDef = true;
        MoveDef = Pos;
      }
    }
  }

  // A circular dependence.
  if (OrderAfterDef && OrderBeforeUse && MoveUse == MoveDef)
    OrderBeforeUse = false;

  // OrderAfterDef takes precedences over OrderBeforeDef. The latter is due
  // to a loop-carried dependence.
  if (OrderBeforeDef)
    OrderBeforeUse = !OrderAfterDef || (MoveUse > MoveDef);

  // The uncommon case when the instruction order needs to be updated because
  // there is both a use and def.
  if (OrderBeforeUse && OrderAfterDef) {
    SUnit *UseSU = Insts.at(MoveUse);
    SUnit *DefSU = Insts.at(MoveDef);
    if (MoveUse > MoveDef) {
      Insts.erase(Insts.begin() + MoveUse);
      Insts.erase(Insts.begin() + MoveDef);
    } else {
      Insts.erase(Insts.begin() + MoveDef);
      Insts.erase(Insts.begin() + MoveUse);
    }
    orderDependence(SSD, UseSU, Insts);
    orderDependence(SSD, SU, Insts);
    orderDependence(SSD, DefSU, Insts);
    return;
  }
  // Put the new instruction first if there is a use in the list. Otherwise,
  // put it at the end of the list.
  if (OrderBeforeUse)
    Insts.push_front(SU);
  else
    Insts.push_back(SU);
}

/// Return true if the scheduled Phi has a loop carried operand.
bool SMSchedule::isLoopCarried(SwingSchedulerDAG *SSD, MachineInstr &Phi) {
  if (!Phi.isPHI())
    return false;
  assert(Phi.isPHI() && "Expecting a Phi.");
  SUnit *DefSU = SSD->getSUnit(&Phi);
  unsigned DefCycle = cycleScheduled(DefSU);
  int DefStage = stageScheduled(DefSU);

  unsigned InitVal = 0;
  unsigned LoopVal = 0;
  getPhiRegs(Phi, Phi.getParent(), InitVal, LoopVal);
  SUnit *UseSU = SSD->getSUnit(MRI.getVRegDef(LoopVal));
  if (!UseSU)
    return true;
  if (UseSU->getInstr()->isPHI())
    return true;
  unsigned LoopCycle = cycleScheduled(UseSU);
  int LoopStage = stageScheduled(UseSU);
  return (LoopCycle > DefCycle) || (LoopStage <= DefStage);
}

/// Return true if the instruction is a definition that is loop carried
/// and defines the use on the next iteration.
///        v1 = phi(v2, v3)
///  (Def) v3 = op v1
///  (MO)   = v1
/// If MO appears before Def, then then v1 and v3 may get assigned to the same
/// register.
bool SMSchedule::isLoopCarriedDefOfUse(SwingSchedulerDAG *SSD,
                                       MachineInstr *Def, MachineOperand &MO) {
  if (!MO.isReg())
    return false;
  if (Def->isPHI())
    return false;
  MachineInstr *Phi = MRI.getVRegDef(MO.getReg());
  if (!Phi || !Phi->isPHI() || Phi->getParent() != Def->getParent())
    return false;
  if (!isLoopCarried(SSD, *Phi))
    return false;
  unsigned LoopReg = getLoopPhiReg(*Phi, Phi->getParent());
  for (unsigned i = 0, e = Def->getNumOperands(); i != e; ++i) {
    MachineOperand &DMO = Def->getOperand(i);
    if (!DMO.isReg() || !DMO.isDef())
      continue;
    if (DMO.getReg() == LoopReg)
      return true;
  }
  return false;
}

// Check if the generated schedule is valid. This function checks if
// an instruction that uses a physical register is scheduled in a
// different stage than the definition. The pipeliner does not handle
// physical register values that may cross a basic block boundary.
bool SMSchedule::isValidSchedule(SwingSchedulerDAG *SSD) {
  for (int i = 0, e = SSD->SUnits.size(); i < e; ++i) {
    SUnit &SU = SSD->SUnits[i];
    if (!SU.hasPhysRegDefs)
      continue;
    int StageDef = stageScheduled(&SU);
    assert(StageDef != -1 && "Instruction should have been scheduled.");
    for (auto &SI : SU.Succs)
      if (SI.isAssignedRegDep())
        if (Register::isPhysicalRegister(SI.getReg()))
          if (stageScheduled(SI.getSUnit()) != StageDef)
            return false;
  }
  return true;
}

/// A property of the node order in swing-modulo-scheduling is
/// that for nodes outside circuits the following holds:
/// none of them is scheduled after both a successor and a
/// predecessor.
/// The method below checks whether the property is met.
/// If not, debug information is printed and statistics information updated.
/// Note that we do not use an assert statement.
/// The reason is that although an invalid node oder may prevent
/// the pipeliner from finding a pipelined schedule for arbitrary II,
/// it does not lead to the generation of incorrect code.
void SwingSchedulerDAG::checkValidNodeOrder(const NodeSetType &Circuits) const {

  // a sorted vector that maps each SUnit to its index in the NodeOrder
  typedef std::pair<SUnit *, unsigned> UnitIndex;
  std::vector<UnitIndex> Indices(NodeOrder.size(), std::make_pair(nullptr, 0));

  for (unsigned i = 0, s = NodeOrder.size(); i < s; ++i)
    Indices.push_back(std::make_pair(NodeOrder[i], i));

  auto CompareKey = [](UnitIndex i1, UnitIndex i2) {
    return std::get<0>(i1) < std::get<0>(i2);
  };

  // sort, so that we can perform a binary search
  llvm::sort(Indices, CompareKey);

  bool Valid = true;
  (void)Valid;
  // for each SUnit in the NodeOrder, check whether
  // it appears after both a successor and a predecessor
  // of the SUnit. If this is the case, and the SUnit
  // is not part of circuit, then the NodeOrder is not
  // valid.
  for (unsigned i = 0, s = NodeOrder.size(); i < s; ++i) {
    SUnit *SU = NodeOrder[i];
    unsigned Index = i;

    bool PredBefore = false;
    bool SuccBefore = false;

    SUnit *Succ;
    SUnit *Pred;
    (void)Succ;
    (void)Pred;

    for (SDep &PredEdge : SU->Preds) {
      SUnit *PredSU = PredEdge.getSUnit();
      unsigned PredIndex = std::get<1>(
          *llvm::lower_bound(Indices, std::make_pair(PredSU, 0), CompareKey));
      if (!PredSU->getInstr()->isPHI() && PredIndex < Index) {
        PredBefore = true;
        Pred = PredSU;
        break;
      }
    }

    for (SDep &SuccEdge : SU->Succs) {
      SUnit *SuccSU = SuccEdge.getSUnit();
      // Do not process a boundary node, it was not included in NodeOrder,
      // hence not in Indices either, call to std::lower_bound() below will
      // return Indices.end().
      if (SuccSU->isBoundaryNode())
        continue;
      unsigned SuccIndex = std::get<1>(
          *llvm::lower_bound(Indices, std::make_pair(SuccSU, 0), CompareKey));
      if (!SuccSU->getInstr()->isPHI() && SuccIndex < Index) {
        SuccBefore = true;
        Succ = SuccSU;
        break;
      }
    }

    if (PredBefore && SuccBefore && !SU->getInstr()->isPHI()) {
      // instructions in circuits are allowed to be scheduled
      // after both a successor and predecessor.
      bool InCircuit = llvm::any_of(
          Circuits, [SU](const NodeSet &Circuit) { return Circuit.count(SU); });
      if (InCircuit)
        LLVM_DEBUG(dbgs() << "In a circuit, predecessor ";);
      else {
        Valid = false;
        NumNodeOrderIssues++;
        LLVM_DEBUG(dbgs() << "Predecessor ";);
      }
      LLVM_DEBUG(dbgs() << Pred->NodeNum << " and successor " << Succ->NodeNum
                        << " are scheduled before node " << SU->NodeNum
                        << "\n";);
    }
  }

  LLVM_DEBUG({
    if (!Valid)
      dbgs() << "Invalid node order found!\n";
  });
}

/// Attempt to fix the degenerate cases when the instruction serialization
/// causes the register lifetimes to overlap. For example,
///   p' = store_pi(p, b)
///      = load p, offset
/// In this case p and p' overlap, which means that two registers are needed.
/// Instead, this function changes the load to use p' and updates the offset.
void SwingSchedulerDAG::fixupRegisterOverlaps(std::deque<SUnit *> &Instrs) {
  unsigned OverlapReg = 0;
  unsigned NewBaseReg = 0;
  for (SUnit *SU : Instrs) {
    MachineInstr *MI = SU->getInstr();
    for (unsigned i = 0, e = MI->getNumOperands(); i < e; ++i) {
      const MachineOperand &MO = MI->getOperand(i);
      // Look for an instruction that uses p. The instruction occurs in the
      // same cycle but occurs later in the serialized order.
      if (MO.isReg() && MO.isUse() && MO.getReg() == OverlapReg) {
        // Check that the instruction appears in the InstrChanges structure,
        // which contains instructions that can have the offset updated.
        DenseMap<SUnit *, std::pair<unsigned, int64_t>>::iterator It =
          InstrChanges.find(SU);
        if (It != InstrChanges.end()) {
          unsigned BasePos, OffsetPos;
          // Update the base register and adjust the offset.
          if (TII->getBaseAndOffsetPosition(*MI, BasePos, OffsetPos)) {
            MachineInstr *NewMI = MF.CloneMachineInstr(MI);
            NewMI->getOperand(BasePos).setReg(NewBaseReg);
            int64_t NewOffset =
                MI->getOperand(OffsetPos).getImm() - It->second.second;
            NewMI->getOperand(OffsetPos).setImm(NewOffset);
            SU->setInstr(NewMI);
            MISUnitMap[NewMI] = SU;
            NewMIs[MI] = NewMI;
          }
        }
        OverlapReg = 0;
        NewBaseReg = 0;
        break;
      }
      // Look for an instruction of the form p' = op(p), which uses and defines
      // two virtual registers that get allocated to the same physical register.
      unsigned TiedUseIdx = 0;
      if (MI->isRegTiedToUseOperand(i, &TiedUseIdx)) {
        // OverlapReg is p in the example above.
        OverlapReg = MI->getOperand(TiedUseIdx).getReg();
        // NewBaseReg is p' in the example above.
        NewBaseReg = MI->getOperand(i).getReg();
        break;
      }
    }
  }
}

/// After the schedule has been formed, call this function to combine
/// the instructions from the different stages/cycles.  That is, this
/// function creates a schedule that represents a single iteration.
void SMSchedule::finalizeSchedule(SwingSchedulerDAG *SSD) {
  // Move all instructions to the first stage from later stages.
  for (int cycle = getFirstCycle(); cycle <= getFinalCycle(); ++cycle) {
    for (int stage = 1, lastStage = getMaxStageCount(); stage <= lastStage;
         ++stage) {
      std::deque<SUnit *> &cycleInstrs =
          ScheduledInstrs[cycle + (stage * InitiationInterval)];
      for (std::deque<SUnit *>::reverse_iterator I = cycleInstrs.rbegin(),
                                                 E = cycleInstrs.rend();
           I != E; ++I)
        ScheduledInstrs[cycle].push_front(*I);
    }
  }

  // Erase all the elements in the later stages. Only one iteration should
  // remain in the scheduled list, and it contains all the instructions.
  for (int cycle = getFinalCycle() + 1; cycle <= LastCycle; ++cycle)
    ScheduledInstrs.erase(cycle);

  // Change the registers in instruction as specified in the InstrChanges
  // map. We need to use the new registers to create the correct order.
  for (int i = 0, e = SSD->SUnits.size(); i != e; ++i) {
    SUnit *SU = &SSD->SUnits[i];
    SSD->applyInstrChange(SU->getInstr(), *this);
  }

  // Reorder the instructions in each cycle to fix and improve the
  // generated code.
  for (int Cycle = getFirstCycle(), E = getFinalCycle(); Cycle <= E; ++Cycle) {
    std::deque<SUnit *> &cycleInstrs = ScheduledInstrs[Cycle];
    std::deque<SUnit *> newOrderPhi;
    for (unsigned i = 0, e = cycleInstrs.size(); i < e; ++i) {
      SUnit *SU = cycleInstrs[i];
      if (SU->getInstr()->isPHI())
        newOrderPhi.push_back(SU);
    }
    std::deque<SUnit *> newOrderI;
    for (unsigned i = 0, e = cycleInstrs.size(); i < e; ++i) {
      SUnit *SU = cycleInstrs[i];
      if (!SU->getInstr()->isPHI())
        orderDependence(SSD, SU, newOrderI);
    }
    // Replace the old order with the new order.
    cycleInstrs.swap(newOrderPhi);
    cycleInstrs.insert(cycleInstrs.end(), newOrderI.begin(), newOrderI.end());
    SSD->fixupRegisterOverlaps(cycleInstrs);
  }

  LLVM_DEBUG(dump(););
}

void NodeSet::print(raw_ostream &os) const {
  os << "Num nodes " << size() << " rec " << RecMII << " mov " << MaxMOV
     << " depth " << MaxDepth << " col " << Colocate << "\n";
  for (const auto &I : Nodes)
    os << "   SU(" << I->NodeNum << ") " << *(I->getInstr());
  os << "\n";
}

#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
/// Print the schedule information to the given output.
void SMSchedule::print(raw_ostream &os) const {
  // Iterate over each cycle.
  for (int cycle = getFirstCycle(); cycle <= getFinalCycle(); ++cycle) {
    // Iterate over each instruction in the cycle.
    const_sched_iterator cycleInstrs = ScheduledInstrs.find(cycle);
    for (SUnit *CI : cycleInstrs->second) {
      os << "cycle " << cycle << " (" << stageScheduled(CI) << ") ";
      os << "(" << CI->NodeNum << ") ";
      CI->getInstr()->print(os);
      os << "\n";
    }
  }
}

/// Utility function used for debugging to print the schedule.
LLVM_DUMP_METHOD void SMSchedule::dump() const { print(dbgs()); }
LLVM_DUMP_METHOD void NodeSet::dump() const { print(dbgs()); }

#endif

void ResourceManager::initProcResourceVectors(
    const MCSchedModel &SM, SmallVectorImpl<uint64_t> &Masks) {
  unsigned ProcResourceID = 0;

  // We currently limit the resource kinds to 64 and below so that we can use
  // uint64_t for Masks
  assert(SM.getNumProcResourceKinds() < 64 &&
         "Too many kinds of resources, unsupported");
  // Create a unique bitmask for every processor resource unit.
  // Skip resource at index 0, since it always references 'InvalidUnit'.
  Masks.resize(SM.getNumProcResourceKinds());
  for (unsigned I = 1, E = SM.getNumProcResourceKinds(); I < E; ++I) {
    const MCProcResourceDesc &Desc = *SM.getProcResource(I);
    if (Desc.SubUnitsIdxBegin)
      continue;
    Masks[I] = 1ULL << ProcResourceID;
    ProcResourceID++;
  }
  // Create a unique bitmask for every processor resource group.
  for (unsigned I = 1, E = SM.getNumProcResourceKinds(); I < E; ++I) {
    const MCProcResourceDesc &Desc = *SM.getProcResource(I);
    if (!Desc.SubUnitsIdxBegin)
      continue;
    Masks[I] = 1ULL << ProcResourceID;
    for (unsigned U = 0; U < Desc.NumUnits; ++U)
      Masks[I] |= Masks[Desc.SubUnitsIdxBegin[U]];
    ProcResourceID++;
  }
  LLVM_DEBUG({
    if (SwpShowResMask) {
      dbgs() << "ProcResourceDesc:\n";
      for (unsigned I = 1, E = SM.getNumProcResourceKinds(); I < E; ++I) {
        const MCProcResourceDesc *ProcResource = SM.getProcResource(I);
        dbgs() << format(" %16s(%2d): Mask: 0x%08x, NumUnits:%2d\n",
                         ProcResource->Name, I, Masks[I],
                         ProcResource->NumUnits);
      }
      dbgs() << " -----------------\n";
    }
  });
}

bool ResourceManager::canReserveResources(const MCInstrDesc *MID) const {

  LLVM_DEBUG({
    if (SwpDebugResource)
      dbgs() << "canReserveResources:\n";
  });
  if (UseDFA)
    return DFAResources->canReserveResources(MID);

  unsigned InsnClass = MID->getSchedClass();
  const MCSchedClassDesc *SCDesc = SM.getSchedClassDesc(InsnClass);
  if (!SCDesc->isValid()) {
    LLVM_DEBUG({
      dbgs() << "No valid Schedule Class Desc for schedClass!\n";
      dbgs() << "isPseduo:" << MID->isPseudo() << "\n";
    });
    return true;
  }

  const MCWriteProcResEntry *I = STI->getWriteProcResBegin(SCDesc);
  const MCWriteProcResEntry *E = STI->getWriteProcResEnd(SCDesc);
  for (; I != E; ++I) {
    if (!I->Cycles)
      continue;
    const MCProcResourceDesc *ProcResource =
        SM.getProcResource(I->ProcResourceIdx);
    unsigned NumUnits = ProcResource->NumUnits;
    LLVM_DEBUG({
      if (SwpDebugResource)
        dbgs() << format(" %16s(%2d): Count: %2d, NumUnits:%2d, Cycles:%2d\n",
                         ProcResource->Name, I->ProcResourceIdx,
                         ProcResourceCount[I->ProcResourceIdx], NumUnits,
                         I->Cycles);
    });
    if (ProcResourceCount[I->ProcResourceIdx] >= NumUnits)
      return false;
  }
  LLVM_DEBUG(if (SwpDebugResource) dbgs() << "return true\n\n";);
  return true;
}

void ResourceManager::reserveResources(const MCInstrDesc *MID) {
  LLVM_DEBUG({
    if (SwpDebugResource)
      dbgs() << "reserveResources:\n";
  });
  if (UseDFA)
    return DFAResources->reserveResources(MID);

  unsigned InsnClass = MID->getSchedClass();
  const MCSchedClassDesc *SCDesc = SM.getSchedClassDesc(InsnClass);
  if (!SCDesc->isValid()) {
    LLVM_DEBUG({
      dbgs() << "No valid Schedule Class Desc for schedClass!\n";
      dbgs() << "isPseduo:" << MID->isPseudo() << "\n";
    });
    return;
  }
  for (const MCWriteProcResEntry &PRE :
       make_range(STI->getWriteProcResBegin(SCDesc),
                  STI->getWriteProcResEnd(SCDesc))) {
    if (!PRE.Cycles)
      continue;
    ++ProcResourceCount[PRE.ProcResourceIdx];
    LLVM_DEBUG({
      if (SwpDebugResource) {
        const MCProcResourceDesc *ProcResource =
            SM.getProcResource(PRE.ProcResourceIdx);
        dbgs() << format(" %16s(%2d): Count: %2d, NumUnits:%2d, Cycles:%2d\n",
                         ProcResource->Name, PRE.ProcResourceIdx,
                         ProcResourceCount[PRE.ProcResourceIdx],
                         ProcResource->NumUnits, PRE.Cycles);
      }
    });
  }
  LLVM_DEBUG({
    if (SwpDebugResource)
      dbgs() << "reserveResources: done!\n\n";
  });
}

bool ResourceManager::canReserveResources(const MachineInstr &MI) const {
  return canReserveResources(&MI.getDesc());
}

void ResourceManager::reserveResources(const MachineInstr &MI) {
  return reserveResources(&MI.getDesc());
}

void ResourceManager::clearResources() {
  if (UseDFA)
    return DFAResources->clearResources();
  std::fill(ProcResourceCount.begin(), ProcResourceCount.end(), 0);
}